Dems don't want to win.
Not as their first priority at least.
They want ~~money~~ funding.
Winning too much would hurt their bottom lines, both because being "the resistance" every so often brings in more donations and because listening to the public over monied interests would alienate them from those monied interests, and their donations.

This is also why they didn't definitively nullify the Comstock act or codify Roe v Wade when they had the chance. Because actually solving the problem means they can't campaign, and fundraise, on perennially preventing the problem.

Edit: forgot to actually get to the point lol, Biden would never, ahem, definitively, stop, Trump, because he doesn't have any reason to. He would then get a new opponent it would be harder to use the threat of to fundraise.
Trump is a fantastic heel for them and the Dem establishment would never actually stop stop him because it would then slow down the donations.