They know very well their votes have been stolen for decades...LBJ set the expectation that blacks would vote democrat for the next 200 years after the Civil Rights Bill passed. That was carte blanche to steal the black American vote starting in the 60's. Black vote has declined ever since because of it. I.e. no matter how they vote, they get the same results. Been going on for decades now.
I guess what I'm saying is that if it wasn't for stolen elections for decades, democrats would rarely win. That's how long this has been going on. People by and large just aren't that stupid, especially those in the inner city.