because throughout history, white people have always done wrong to other groups. they've always been the ones with power. the ones who enslaved, raped, abused, and killed people of color.
white people like to throw out that PoC are racist, and that's not true in the least. racism is systematic oppression that takes advantage of people of color economically, politically and socially and the ones who established this racism are the ones with power: white people. as long as white people are running things and are the ones in charge of how everything is run, there will never be actual racism against white people. prejudice, sure. but not racism.
and the jokes we make are almost never as bad as those said by white people to black people, for example. making fun of white girls for going to Starbucks is hardly an insult. we're poking fun of their "stereotypes" but that's nowhere near as bad as seeing a black girl in her teens and saying "I wonder how many kids she has". it's an entirely different animal.
it's because white people have always told us we were wrong or bad or less than simply for being who we are. still to this day, i face racism from white people on almost a daily basis. but white people never really will, so the jokes we make will never be as hard hitting as those said to us by white people.