I suspect the audience of people who really like Cards Against Humanity leans towards people who like being "politically incorrect", because the card game often inspires people to be incredibly offensive. It seems likely that their audience includes lots of 4channers, shitlords, extremists, racists, or any other group of people known to be generally offensive. By making moves like this, they're showing everyone else…
Not quite, it leans towards people who think that being "politically incorrect" is funny. The great thing about CAH is exactly that it should be clear everything is said in jest. It is important in a society to be able to joke about the taboos. And it is great for people that enjoy this kind of humor to have a place for it where people don't suspect you say these things because you mean them.