My own theory (without any real evidence) is that the oligarchs use race to divide the white working class from the non-white working class. A specific example is the video on systemic racism going around. It correctly points out redlining (a truly horrific practice), but also talks about black students having to attend underfunded schools. I attended predominantly black, underfunded, public schools my entire childhood. By this logic, I was at the same schools and was a "victim" of systemic racism. Which immediately implies that it was actually systemic classism at play against the working poor, rather than being purely race-based.
If a party chose to ignore the corporate overlords and focus on issues that working class people of all ethnicities cared about, they would get a lot of votes, and very few super PAC donations.