How come Daesh/ISIS does not attack Israel, who are supposed to be their worst enemy?
Precision: I'm not asking the reason for the other way around, why isn't Israel attacking IS I'm asking why isn't IS threatening a country like Israel which is on a long term mission to divide the Arab world.
I think there may be a couple of components to this
Israel has excellent defenses and is very strict regarding points of entry into their territory. It's plausible that DAESH has attempted to penetrate and Israel has detained those individuals as high risk, which they do without trial on a regular basis when it comes to Palestinians.
Israel is not waging open warfare on DAESH at the urging of the US State Department it is rumored. The US is concerned that a coalition revolving around a fight with DAESH would be compromised if the coalition included Israel, hence the lack of air strikes from Israel.
DAESH has warned Israel in December of 2015 that they will inject themselves into Palestine and established an Islamic State to include it.
There are a variety of reasons:
ISIS is quite happy with the status quo of Israel attacking, or at least putting pressure on, their main tactical enemies (Shia block in general, in the personification of Hezbollah). If it wasn't for Israel, Hezbollah could have sent a significantly more overwhelming force from Lebanon into Syria.
ISIS has a finite amount of resources. Attacking Israel simply doesn't amount to rational expenditure of said resources to achieve either their tactical goals (establishment of Caliphate) or strategic goals (Triggering apocalyptic conflict with "Rome"). It may offer minor propaganda and morale value, but not nearly enough compared to attacks in Europe.
As another answer alluded to, inspiring local attackers is difficult for them since they are competing ideologically with other Islamist influences (full spectrum from FATEH on less extreme end, on to HAMAS on to Islamic Jihad) which are all locally entrenched. It's far easier to gain an ISIS follower who isn't already committed to competing - and differently goaled - movement.
ISIS seems to have two ways of attacking. In Iraq and Syria, they recruited disaffected Muslims and integrated them into an occupying force that operates locally. Outside of Iraq and Syria, they do not have enough recruits to engage in occupation. They can only encourage terrorists acts. They do this through a combination of internet engagement (e.g. San Bernardino) and direct engagement with people who go to Iraq or Syria to train with them (Paris and Brussels).
I would guess that they haven't (yet) engaged with Muslims in Palestine to occupy territory. And the Israelis already are suspicious of Muslims in Israel. Muslims in Israel don't have the freedom of action that those in the USA and Europe have. This makes it difficult to engage in terrorist attacks.
It's even possible that there have been ISIS attacks in Israel but that they were insufficiently successful to be worth claiming. There is certainly enough conflict there that violent attacks might easily be explained without ISIS. Or ISIS hasn't been able to engage with disaffected Muslims in Israel because they have already joined other groups. Wikipedia lists Hamas as opposing ISIS.
You might also ask why they don't take the occupying forces from Iraq and Syria and go to Israel. The most likely reason is that the areas they occupy aren't that close to Israel. Syria doesn't have much of a border with Israel and Assad's forces are between ISIS and Israel. And of course, if they left their current territory, they might lose it. Perhaps things would change if they defeated Assad.
In a nutshell, Saudi Arabia is a fundamentally theocratic islamic country that is allegedly helping DAESH. They share the same 'ethos' and non-democratic approach to anything, from public executions to women. Saudi Arabia and Israel are friendlies, now it is also stated by the Israeli PM Benjamin Netanyahu 'Israel and Saudi Arabia are allies'.
DAESH have the ambition to establish a state. The military actions they take is part of that goal (to keep and expand their territory). Considering that Israel is the local military superpower a direct attack would be suicide.
The terrorist actions have the goal of triggering suppression of Muslims in those countries and they think that will make them more willing to help DAESH. So the targets for terrorist attacks will be places with a quite large, but well integrated Muslim population. Israel does not match that.
DAESH is still at war in Syria. So they don't have the capabilities (yet) to attack another country. Also knowing that it will be harder to win territory over a well trained and equipped army. I'm interpreting the question as an army kind of attack. Not terrorist attacks, separated in time and place.
If your question is about terrorist attacks (or regardless of type of attack). Then I think the other answers about the influence of hamas, fateh and saudi arabia and the conflict with DAESH could be the reason.
ISIL stands for "Islamic State of Iraq and Levant". ISIS/ISIL/DAESH inherently claims of territory in the Levant, hence, an entire territory of Israel.
BTW, many Israeli politicians oppose calling Islamic State as "ISIL" specifically for this very reason. They prefer "ISIS" or "DAESH" instead.
Another thing is that they, for some reason, don't target Israel as their first-order target.
The actual reasoning is usually hard to tell for sure, since we don't know what's on people's mind till they declare something or act accordingly. However, one may speculate that maybe ISIS leaders realize that:
I think It is not because "Israel has excellent defenses"; since if DAESH want to attack or at least threathen Israel they can do it as Hamas did. Hamas is weaker than DAESH, but they did so.
Israel is the worst enemy of Muslims so attacking Israel rise popularity of DAESH. but DAESH does not attack. Why? because:
As Noor says: The ideology DAESH follows, stems from Wahhabism, which was established in Saudi Arabia by the British Government. Saudi Arabia is common friend of both. British Government is father of Israel and grandfather of DAESH.
If DAESH attack Israel then they become an enemy for U.S, U.K, and all E.U, which I think this is not the case now (Just compare "what Russia did against DAESH in Syria" with "what U.S, U.K, and all E.U did against DAESH in Syria and Iraq"). So DAESH Loses probable hidden support of them. Then DAESH Loses Logistics support of Turkey. No need to say: If DAESH become an enemy for U.S, then Saudi Arabia (which is footboy of U.S) can not support them financially.
Updeate:
Here is a statement about creation of DAESH, which I am not sure if this is a fact, but i add to my answer. If I find evidence for validity, I add it; If not I remove the update:
see TRUMP: 'Hillary Clinton created ISIS with Obama'
and this
How come Daesh/ISIS does not attack Israel, who are supposed to be their worst enemy?...
I think your analysis is pretty crude - to put it mildly. I'm not a student of middle east politics; however, Michael Jansen at the Jordan Times has this to say on Feb 7, 2018:
Israel is inadvisably but increasingly involved in conflicts raging in its northern and southern neighbours. In the north, Israel has for several years provided aid and comfort to Daesh, Al Qaeda, and other insurgents fighting the Syrian government. This began by offering medical treatment to anti-government fighters and gradually involved ministering to wounded civilians, offering humanitarian aid, and paying fighters' salaries.
Isn't this already surprising? I mean, 'providing aid and comfort to Daesh and Al Qaeda'; they also add:
The following is for Ugoren who didn't bother to read the article but was upset I was quoting an Arabic newspaper.
Nour Samaha, writing on The Intercept website on January 23, revealed that Israel intends to create a "safe zone" by expanding the buffer zone along the occupied Golan Heights into the Syrian provinces of Quneitra and Daraa. Justification for Israel's latest land-grab in Syria is its determination that the Israeli army must not confront the Syrian army, Iranian-backed Shiite militias and Lebanon's Hizbollah fighters along the Golan ceasefire line...
And
It is ironic, therefore, that Israel is bombing Daesh in Egypt while supporting Daesh in Syria. Preserving Daesh and allied taqfiris as an "asset" anywhere is a dangerous, cynical game which will have fresh "unintended consequences" for Israel and for its allies in the approving West.
Just from this we can see that the situation is quite a bit more complex that you're supposing it to be.
