1. Christianity of some flavor is the dominant religion in the west by a huge margin. Media can make fun of Christians safely because it is punching up. Punching up is pretty safe. Pick on any other religion and you are punching down. Punching down when it comes to identity is pretty dangerous.
2. A minority of Christians loudly do very un-Christian things in the name of Christ. You won't see people making light of faith based organizations that feed the poor. You WILL see people making fun of evangelical ministers with private jets. I'm not a Christian or a bibilical scholar, but I have a hard time believing that Jesus would approve of a lot of the more right-leaning American christians.