Why did the Arab spring back a few years ago fail for the most part, the Iranian green movement didn't get the result it wanted, but the European revolutions (such as French revolution in part or revolutions of 1848) were able to reform a continent with conservative religious views and a set of dictatorship governments into a significantly more free and liberal region?
History and Politics rarely accommodate with clear binary outcome. So, as much I would not say that the Arab Spring revolutions weren't a failure as a whole, I would also not say that the European ones were fully a success.
The European/American revolutions were not fully successful...
A revolution usually stem from a group of people unhappy about the current regime. They need to be strong enough to take out the regime, but to make it successful, they need to be clear what the desired outcome is. In that sense the American Revolution was successful in building a new independent country. But they failed to extend it to Canada. And whether it was the original intended purpose is also doubtful.
The French Revolution of 1789 was meant to imitate the English one from a century before. The purpose of many factions was to bring down absolutism, not all were in favour of a Republic. In any case, after the first struggle, the new governments had several phases like the Terror, where it was easy to lose one's head. Arguably, the French revolution could be considered achieved when Napoleon took the power with a Coup d'Etat, after about 10 years. Was it really a success?
In the comments, Bobson mentioned the Revolutions of 1848 as a resemblance to the 2011 revolutions in some Arab countries. But the Wikipedia page summarised it quite well,
So, were they really successful?
What the previously mentioned revolutions did succeed in, was to set some examples, some ideas, propose some alternative, which, in some case lead to some changes years later. Without the French Revolutions of 1789 and 1848, France probably wouldn't have been a Republic. Which it really achieved in 1871. And even at that time, there were discussions of bringing a King back.
... and the 2011 Revolutions weren't complete failure neither.
In 2016 you want to judge fully the outcome of those protests, revolutions, wars. It is probably too early.
Furthermore, if the revolution idea spread like a wave (partly due to Social Networks), the reality of each country is different. The causes and means were also quite different. To give a few examples
Depending on the metric you want to go by, those may or may not qualify as success. Many did bring political changes and often removed the dictatorship government that was in place.
Revolutions tend to fail rather often. Depending on your idea of what a success is, you could even say that no revolution ever achieved its goals in full - it's kind of hard when most revolutions were spearheaded by multiple groups with conflicting interests in the first place, and this applies to Arab Spring as easily as it does to the French Revolution.
"Revolution" doesn't mean "fight for freedom". Most revolutions were anything but, either in spirit or in execution. It simply means a fight to change the government / leading powers etc. - sometimes that means changing them for a democracy, both most of the time it's simply replacing one dictator for another (or one "democracy" for another "democracy" :P).
If you only include revolutions that declared a fight for freedom, you still have plenty that have a different idea of what freedom is e.g. freedom to do whatever doesn't conflict with others, freedom to comfortable life while someone else pays for your expenses or even freedom to live under a Christian dictatorship.
Even if you agree on what freedom means, the revolution rarely results in even that - the most common tendency is simply to replace the head(s) of the government, without any real change. French revolution was a great example of a reign of terror caused by the rebels "winning". The Hussite wars were about religious freedom, but they resulted in plenty of theocratic regions and caused a lot of damage to innocents. The American Revolution worked out well enough, but they never really had the full fledged bureaucratic structure to overthrow - they just wanted to get rid of their de iure overlords (and the taxes, tariffs and laws they didn't feel were fair, especially given their lack of representation), and there were still plenty of voices calling for a similar government, because this new-fangled freedom thing sounded new and dangerous. And as Monty Harder noted in the other answer, it was really a war of seccession rather than a revolution - there was never a goal of overthrowing the British government, just separating from it. The same is true of many "revolutions", including some that can be considered part of the Arab Spring - for example, the Kurd seccession efforts.
In the end, history is written by the victors. The Russian Bolshevik revolution was hailed as a succesful revolution, and was like that in the history books, but you'd be hard pressed to find any "common people" who profited from it - only the people in charge really changed, and most things just got worse. Sure, they got rid of the Czar, so the revolution succeeded - but it wasn't really a change for the better, so would you call that revolution successful? If so, plenty of the Arab Spring revolutions were "successful" as well, and some are still in progress. It's not like the French Revolution was just people raising and saying "Enough!" - they took up arms, and fought long and hard. Peaceful revolutions do exist, but they're quite rare - and usually build on a situation that's de facto already quite close to what the revolutionists are trying to enforce de iure.
Did they fail — and did Europeans succeed? First, I'm sure there are plenty who wished for a more conservative Islamic rule and to further distance themselves from the West during the Arab spring — and they got what they wanted!
When we look at the European revolutions... Lets take the French... The goal was "equality, liberty and fraternity", and to get rid of the chains of the Church, the Aristocracy and the King. In the long term, they succeeded in much of this; but one could claim that until very recent, they just swapped one chain from another. Rather than being beholden to their King and local lords, most became "serfs" of the local money-holders — those who could buy up land, own factories, offer jobs. Any rights for the working-class and any fair trade of money for work — and then money for products — is far from automatic. Nor did the revolution give people more food on the table.
If we look more immediately, The French Revolution ended with a reign of terror and an absence of justice, much worse than what the King had done. And within a few years, there sat an Emperor on the French throne — which would lead the country into war, calamity and starvation. And later, they got another King.
And while some — like those who had or could get money — made out well, other groups stood still or even back-slid because of the revolution. And some groups — especially women — had to wait very long for the promised "equality".
The end of the "Socialist revolution" ended with dictatorships. The end of the Communist bloc, ended with poverty and raging, uncontrolled capitalism and crime-syndicates — not much democracy. And if we look at Putin's Russia, they're on the way back to dictatorship — and possibly a new "Tsar".
The American Revolution — which started with declaring that people not only could rebel against an oppressive Government, but that they actually had a duty to do so — have ended with Government that wants to surveil its citizens 24/7 and to know all their secrets. It forces its will upon the world, and has coupled Christianity to itself in a way that's starting to become disturbing. And less said about the current election-cycle, the better...
So I'd say that the Arab Spring isn't worse — nor European Revolutions better — than revolutions in general.
There were a lot of revolutions across Europe in 1848, and many of them failed/were crushed. There has been some revolutions in the arab spring which relatively succeeded (Tunisia), and some other were crushed. Just like in Europe.
"Did they fail — they succeed", answers above (which could be longer), show that your assumption is not correct. But I want to add some points:
If we see a revolution or a movement (Arab spring, 99%,...) stopped, it doesn't mean it is failed completely. The protesters are living in the country, some of them satisfied (by media, government arguments,...) some not; The more a government is sever, the more people will be unsatisfied. The revolution movement could resume any time.
The "Arab spring" suffered from lack of leadership.
Some reasons differs case by case: