Yes. 2014 was peak ISIS strength too. France has a big Muslim population, so that's also why. But also. We're not really allowed to ask the question "What does ISIS want?" So they're just like every other Disney villain, doing bad things because their souls are rotten or something. But the history is more complex than that and you can't have such big support built on pure irrationality.

Their methods are obviously terrorist, and that's their biggest problem, so I'm not defending anyone here. But here's the very gist of it: ISIS wants a restoration of the Ottoman Empire, which joined WWI on the side of the Axis and then was "Balkanized" by the Allies in the aftermath. So basically a powerful nation was cut with a ruler into a bunch of weak colonial states that never existed before. Just from that, you get a powerful cultural impetus to restore the former glory, to make the decadent West pay for the humiliation, the hate of Israel, but also of more moderate (shia) factions of Islam.

So on the religious front, ISIS favors a very literal interpretation of Koran, selective too, and consider other interpretations and interpreters their enemies too. Not a good way to make friends all around. Plus, ISIS has a strong propaganda effort. US helped a lot forming the movement by doing what they did in Iraq, Libya, Syria etc. To say nothing, again, about what Europeans did in the region before and together with the US after. ISIS minister of economy, if I'm not mistaken, is (was?) an Australian banker. They recruit widely, it's not just those deranged people cutting people's heads in videos. Many former army personnel that got defeated by the US in Iraq in 2003 is (was?) ISIS. Aleppo showed that they are good at war, they're not dilettantes with machetes. This must be attractive to a certain type of person too. All that is to say: yes, there are people who ideologically identify. Much much less now, obviously, but this won't go away easily because at the root of the movement is a historical humiliation.