Our declared enemies are perfectly straightforward in their stated goals, and their actions are consistent with their words. They select their targets with some care. For a while, it was Europe's Jews, at a Brussels museum and a Toulouse school and a Copenhagen synagogue and a Paris kosher supermarket. But Continentals are, except for political photo-ops on Holocaust Memorial Day, relatively heartless about dead Jews, and wrote off such incidents as something to do with "Israeli settlements" and "occupation" and of no broader significance.
So they moved on to slaughter 49 gays in a nightclub in Orlando - the biggest mound of gay corpses ever piled up in American history and the worst terror attack on American soil since 9/11. But all the usual noisy LGBTQWERTY activists fell suddenly silent, as if they'd all gone back in the closet and curled up in the fetal position. And those Democrats who felt obliged to weigh in thought it was something to do with the need for gun control...
So they targeted provocative expressions of the infidel's abominable false religion, decapitating a French priest at Mass and mowing down pedestrians at a Berlin Christmas market. But post-Christian Europe takes Christianity less seriously than its enemies do, and so that too merited little more than a shrug and a pledge to carry on.
So they selected symbols of nationhood, like France's Bastille Day, Canada's Cenotaph, and the Mother of Parliaments in London. But taking seriously assaults on your own nation's symbols would require you to take your nation seriously, and most western citizens are disinclined to do so. As the great universal talismanic anthem of the age has it, "Imagine there's no countries/It's easy if you try..."
So the new Caliphate's believers figured out that what their enemy really likes is consumerism and pop music. Hence the attacks on the Champs-Élysées and the flagship Åhléns department store in Stockholm, and the bloodbath at the Eagles of Death Metal concert in Paris and now at Ariana Grande's "Dangerous Woman" tour.