They don't need people to travel to Europe, they have brainwashed people who'll do it after some basic training online and a smuggled weapon. Israel doesn't have a large multicultural community that the attackers can pretend to be a part of while plotting an attack/before executing an attack - they'll be searched dozens of times a day just for being 'foreign'. Israel is a total fortress - there are checkpoint everywhere and you can't smuggle weapons in or buy/smuggle whatever it is that you need to make a bomb. Terrorists choose 'soft' targets, places that have no security like beaches, bars and little offices. In London they chose the softest targets ever like tube stations and buses - its like kicking a baby, honestly they aren't interested (they're too cowardly) in surviving and eventually going to jail and that's why they choose the easiest targets.