Maybe because it's a continent, as well as USA, that's been making profit of middle east's misery since forever. That makes them easy for this guys to convince people to commit attacks. Imagine you are a middle eastern child. You see how your family dies because of a war in which Europe takes part. Maybe a western soldier kills them, maybe a guy from your own country kills them, but you are child, you just see all this shit going around you without understanding what's really going on. Your house is destroyed and you have no one left to take care of you. You get traumatized and your psyche breaks down. When things settle down a little, someone takes you under his wings. Perhaps the first person to show some mercy to you after all that suffering. He starts telling you that all this happened because the western world blah blah and that our religion blah blah blah and we have to blah blah blah. This kid is now in it's twenties. What do you expect that he will do?
Or maybe because war is a business. Some companies provide terrorists with means to do this atrocities, people's lust for vengeance increases and countries go to war. Some companies supply the terrorists, others supply the countries. Where do you think ISIS gets all it's supplies? Pretty sure they don't manufacture them themselves. As long as the river of money keeps flowing and everyone gets their cut no cares what happens. But then we act surprised when someone starts shooting with an ak-47 in Paris CBD.
Or maybe the war is because of the resources. Africa has tons of Muslim countries, yet they are not at war with anyone but there own internal forces. Why? Because Africa has no resources at all. The only profit to be made is to sell them machetes. Oil on the other hand is what keeps the world moving. What fuels our cars. What produces most commercial plastics used in countless of applications. What produces our electricity. What makes all the world logistics possible. Whoever that controls oil, controls the world today.
Or maybe we got to the point where it's such a clusterfuck that a combination of all factors and we have already lost track of it all.
/me takes his tinfoil hat off