You have to keep in mind that there's a number of logistical hurdles that they have to jump through in Europe in order to get explosives or guns. So for example, the Villejuif shooter in April 2015 who planned to attack a church: According to French press reports, he was instructed by ISIS to go to a sandwich shop, and the weapons would be waiting for him in a car parked outside. He was just told the make of the car, told to go there, told to pick them up. Putting that kind of attack together, using encrypted communications or other means, is not easy.
