Communists don't have a monopoly on "the left". There are socialist liberals who also fought for these things, not just communists.

There was a time when "centrists" were largely Republican. Many of them have jumped ship due to Trumpism, so they are now part of the very mixed coalition that is the Democratic Party. Problem is we were so focused on fighting each other that we forgot to fight the fascist fucks on the other side of the aisle.