Do we have a reliable statistic that provides an empirical observation of the kind "dictators tend to hold longer speeches than democratically elected politicians; median seems to be 2.341 hours for dictators but only 1.582 hours for elected politicians"?
After all, finding an explanation for a thing 'that's not the case' is usually moot.
And here: The premise might be a bit flawed:
Source: The American Presidency Project / Graphic: Jiachuan Wu / NBC News FEB 5 2019, 10:38 PM ET
Are there correlations tied to one of the speakers being perceived as more 'autocratic'/'authoritarian' (perceived tendencies!)?
Or is 'date of speech' a better explanation for these?
And the longest speech in such a context:
1) India’s former finance minister V.K. Krishna Menon’s speech in 1957 explaining India’s position on Kashmir for over seven hours is listed in the Guinness Book of Records as the longest speech delivered at the United Nations (UN).
(2) The second longest speech at an international forum is again at the UN and was delivered by Cuban leader Fidel Castro in 1960. It lasted four hours and 29 minutes. Castro bettered his own record in 1986 when he spoke for seven hours in Cuba.
That gives two outliers for speech length, the nominally democratic one being longer than the one by a dictatorial speaker?
Foreign Policy investigated this question and presented a summary of theories:
In 2009, after Libyan dictator Muammar al-Qaddafi’s 96-minute speech before the United Nations, the BBC investigated this very question. The article notes that marathon speeches by democratic leaders — such as one Indian politician’s eight-hour Kashmir lecture in 1957 — are rare, and that applause (out of either genuine passion or fear for one’s life) often accounts for a substantial portion of history’s longest speeches. The BBC even highlights an amusing example from Russia’s own Stalin, who received a standing ovation that took up a whole side of a vinyl recording of one of his speeches. But another historian argues that long speeches haven’t always been the sole preserve of dictatorships:
"Now [a long speech] is seen as a sign of political weakness, for example Neil Kinnock or Gordon Brown when he uses too many words and too much jargon.
"But earlier generations, ending with Harold Macmillan, had a taste for very long speeches which demonstrated their learning. We have now less patience with people who show their authority by speaking at great length."
One could certainly devote an academic paper to the nuanced relationship between democracy and speech length, but perhaps a simpler explanation exists. As Robert Service, a professor of Russian Studies at Oxford University told the BBC, "You are only ever going to get long speeches when the speaker doesn’t have to worry about the audience running away."
Any other theories?
Update: A number of readers have weighed in on the question of why authoritarian leaders tend to talk for so long. Below are a few of the more interesting suggestions:
"only their opinion matters?" – Facebook user Charles Ursenbach
"Dictatorships also have fewer things competing for viewers’ attention, as the ‘running away’ joke denotes. While the State of the Union is going on, I can switch to a lot of other things, or even watch something in the DVR." – Commenter Pdubble
"It’s probably the most democratic thing Putin does. People call in, ask him questions, some easy to answer, others not so much." – Facebook user Pavel Shmelov
"Because brevity is the soul of wit – and they are, by and large, witless." – Facebook user Julian De Wette.
"Filibusters come to mind, and the[n] immediately the relationship between democracy and speech length mentioned above." – Commenter Zhangir K S
To the "any other theories", I'd add that it seems to be dependent on individual constitution.
Kim Jong-Un seems to be a moderate on that scale: Kim Jong Un's 2019 New Year Address. Only 5515 words in English translation, clocking in at an estimated 43 minutes.
William Henry Harrison had his inaugural address measured at 8445 words, giving an estimated 65 minutes. (All inaugural addresses here, summary: it varies a lot).
Now, thinking dictator, a moustache pops up in everyone's mind.
Speech at 15. Oktober 1933: Bei der Grundsteinlegung zum Haus der Deutschen Kunst in München. 815 words, estimated at 7 minutes.
His explanation for attacking the Soviet Union: 3430 words, estimated at 27 minutes.
A speech on art in front of the party at Nuremberg rally, where he really had all the time and only fans in front of him: 6373 words, estimated 49 minutes.
This man alone could cut it short or ramble on. What is the pattern? Is there one for this single orator alone?
Before anybody jumps in with "yeah, but only communists are evil, what about communist speech length?" –– Look at Lenin and find me a really long speech.
Dig through the archives for Castro's speeches. Then explain why for example his speech at Mass Rally Held Santiago De Cuba 1959–12–01 should be counted as 'dictatorially typically long', as it's only 473 words long?
Let's stop here and remind us of the effect of figure–ground (perception) as applied to news bits and anecdotal statistics from the top of a head.
Let's instead ask "where's the beef"?
Are dictators really long winded speakers on average or on median speech length? Compared to other orators? Systematically enough to even establish a significant correlation?
Gavin Newsom, mayor of San Francisco, liked to speak on "The State of the City. Well, as mayor he had to? But did he really have to do that for 8 hours? Just because he is such a dictator?
This answer maintains that it's needed to establish "it is like that" before starting to explain "why"!
After looking around quite a bit, I didn't find any one such statistic. But quite a lot of counterexamples.
This is intended to be a frame-challenge, or in different words an answer that attempts to put the question from head to its feet.
Coming straight from the question as asked: It seems to be just the other way around: the premise needs a more solid base to convince anyone on a factual angle, not just from impressions based on watching news and remembering some isolated records, like Castro, and then jumping to generalisation from there.
Above I just list examples that show "no fit". If that reduces your conviction on "valid premise", the first step is taken.
Someone needs to provide a convincing statistic that establishes baseline. A baseline on dictators speaking longer on average compared to western democratic leaders?
Otherwise the real question to be answered would be "why do we have the impression of 'dictators being talkative in speeches'"? –– Or: "What are pros and cons for anyone giving a long speech?"
In light of the conflicting information provided above, that would dispute the base claim, the answer here seems to be that Trump or Newsom are reported with the attributes "president" or "mayor", if not just by names only. While foreign leaders with such a bad standing to current leadership in ones own country are labelled "dictator", consequently, and as such this framing and connection of two concepts "dictator" and "long speech" re-inforce a cognitive bias that now begs for explanation, even if reality would not warrant such an investigation.