Because it's all a big act to show how sensitive they are.
In reality very few actually give a shit about black people, nor would they want to do any actual work in their communities. It's just more fun to protest, hold signs, post pics of yourself on Instagram, and rant on Twitter about how outraged you are.
Then go back to conservative Mommy and Daddy they're rebelling against, and ask when this month's allowance is coming.