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...
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.