Gore won the votes in election. The system wouldn't let him claim the win.
Yes, Obama gave a us the terrible ACA, which was drastically less than it should have been. He also abandoned most of his lefty campaign promses, and basically ran as a Republican, as he himself admitted. So yes, lefties didn't show up after that. Why would lefties be happy about a supposedly leftist candidate who self admittedly ran like a Republican?
Hillary lost because she is cartoonishly evil, and clearly campaigned on things that she had no intention of doing. She is practically the embodiment of the lying Corporate Democrats, so I don't see why you think she would get votes from the left.
Biden barely won when Trump was at his lowest. It took our lowest-approval rated president, at his worst time, for Biden to win. And once Biden got into office, he ran mostly to the right, with a few small leftist things sprinkled in. His approval kept declining as he continued to do right-wing things. Why you think a right-wing running president should expect to get votes from the left is beyond me.
Harris said she approved of, and would continue with Biden's mostly right-wing policies, all while chasing to the right after Trump.
You keep saying that leftists don't show up, but then point to mostly right-wing politicians, who run mostly right-wing campaigns and policies as your evidence. Meanwhile, actual leftists keep gaining popularity. We have plenty of evidence of voters showing up for the left, but we don't have evidence of politicians actually doing lefty things. It seems logical to me that when politicians pretend they are on the left, but end up moving to the right, that leftist-voters don't show up for them.