Cause you gotta take the bad with the good?
Basically, the leftists (democrats) know that making their voters lives a hot mess works for them.
Their voters are too stupid, ignorant and lazy to do any real thinking about why their lives and environment (city, neighborhood, state) is such a catastrophe. Instead, they just take the path of least resistance which is to believe what the media and their leaders tell them: It’s republicans and white people that are all the problem.
As a result, importing crime in the form of young, uncivilized males is a big win for them, but importing civilized, educated people that might make their voters lives better is a big loser for them.