Addressing grievances (real or imagined) doesn't always consist of exclusively concentrating on the biggest scoundrel (real or imagined, again).
It's more a matter of opportunity.
As 9/11 should show both in presenting the most promising so far, as well as having given rise to decreasing opportunity as much as possible ever since.
When the disgruntled are more happy about lashing out than about discerning who is the most deserving (again, real or imagined), going utterly indiscriminate is hardly a novelty.
In the context of which the idea of seeing Europe as some nation like the US is highly misleading.
As such Islamic terror in France may appear totally the same as that in Spain, Germany or UK (to name just those), yet has a completely different background and generally speaking (exceptions serving to confirm the rule) a completely different set of perps (culturally). Which can be said for most European countries and let's not even start on Russia.
That the lines between motivations of Islamic terror groups will blur goes without saying and is the stated goal of IS.
Apart from all of which the geography favors Europe (both East and West) opportunity-wise over the US when it comes to accessibility. Where one can walk all the way from Syia or Iraq to France (hurdles notwithstanding), swimming the Atlantic is a bit of a drag.
And as far as recruiting the local help (i.e. Muslims already in sitio), it'll generally depend on the level of disenchantment the more promising cases feel in their particular society of dwelling. As such France probably leads the way in Western Europe (at least), in providing its Maghreb immigrants with the greatest amount of frustration.
A factor that is of course (or potentially will be) exacerbated by the number of Muslims already within a given society.
Nevertheless, to address the issue of "integration", France has less Muslims than UK, but has suffered far more Islamic terror attacks than the latter and also shows a higher fatality number caused. And where Germany has around a quarter less than France, she kind of of fades completely into the background (statistically speaking) when it comes to actual victims.
That Spain ranges high on the list is basically due to 1 (one) notable attack of meanwhile 13 years ago, where the perps managed to kill over 190. There have been single incidents since (often foiled) but none of such magnitude.
And even the London subway bombings of twelve years ago still show double the number of casualties of the recent Manchester tragedy.
Of course such "numbers games" may please statisticians more than they serve as a basis for drawing salient conclusions. It's just that speaking of "Europe" as such an amorphous entity as one wishes to make "Muslims" as being is not at all helpful.
It's already been aptly (and thankfully) addressed that the highest number of victims of Islamic terrorism occurs far, far away among the very Muslims themselves.