As I said before (But maybe in a way that was too difficult for you to understand. I apologise for that) it's because Christians are not only the majority religion in the US, but are also often the most vocal and assertive about their faith in the social and political sphere. So they get targeted disproportionately more then other less popular religions in the country simpley by the virtue of being more abundant and outspoken.
And no, this post doesn't translate to 'Lol they have it coming, stupid Christ lovers', I'm simply putting forth my own idea as to why Christians appear to be 'targeted ' more in our media for being bigots. I'm not a fan of the 'broad brush' either, I don't think all Christians are bad people the same way I don't think all Jews, Pagans, Muslims or Athiests are bad either even if each of their own religions(or lack of) has their share of backwards-ass morons.