It's a safe haven enemy for them, even though Islam is far more anti-LGBT than Christianity they don't dare mock Islam because as we saw with Charlie Hebdo muslims don't fuck around with their religion being mocked, and if you're part of the alphabet people and mocking Islam the result wouldn't be pretty and they're well aware of that.
So they go for the easy religion to mock.
Ironically the left pretends to sees Christianity as more of a boogey man than Islam not because they believe that, but because they're a far safer religion to shit on and criticize. If you draw a picture mocking Jesus at a newspaper its a safe bet 12 employees won't be massacred afterwards.