Because it's tribal I imagine. You can't make a show called Dear Black People and point out things you don't like in their culture without being called a tribal. Works both ways.
ehh... there are real reasons its more acceptable for african americans to do this sort of thing. i don't personally agree but white people are undeniably better off in this country and are a vast majority, so it's not as harmful for someone to take up a 'sassy' attitude towards them. if a white dude was in china i think it would be okay for him to be like "Dear Asians, please stop doing x".
I don't approve of either, and I personally don't think this looks interesting or funny. I'm just saying why this isn't a perfect equivalence.