You're arguing against your own masturbatory fantasy.
The left came out and voted for Harris. They held their nose and voted for the shit pile centrist, as they always do. We've seen with Mamdani that this loyalty is a one way street. Progressives hold their nose and vote for centrists, but centrists do not return the favor.
Harris lost because she couldn't drive enough politically unaligned, low-engagement voters to the polls. The average person who isn't that involved in politics simply didn't think it was credible that Harris would improve their lives in any way.
Aside from a few performative tankies, the message I kept reading on lemmy was "I'm going to vote for Harris, but her dog shit policies are going to cost her the election." And those progressive voices were ignored. Their desperate warnings were drowned out by people like yourself, sticking their fingers in their ears and going, "BLAH BLAH BLAH CAN'T HEAR YOU, VOTE BLUE NO MATTER WHO! IT'S YOUR FAULT IF THE FASCISTS WIN, I HOLD NO RESPONSIBILITY HERE!"