Because they are after money, not safety, and Germany told them they are welcome, and of course Germany is probably the best European country to work in. After they saw the amount of refugees, they started the whole quotas thing. But they won't stay in the country they are send to (depending on the country of course), the quotas are more about splitting the paperwork.
And, I know you don't really mean it seriously, but there are easier ways for Islam to send their people to Europe. You don't know if they'll get to Europe (e.g. sinking boats), if they'll be let into Europe, where they'll end up. So yeah, it's easier to recruit some brainless fucker via internet or use people that are already European citizens than send your people to Europe.