I think they're just running on inertia. It seems to me that Dems have done the "means tested [insert popular policy]" or "vague and neglible motion toward [popular policy]" (Infrastructure bill for example) for so long that they've gotten used to less than bare minimum being enough. It seems as though popular sentiment has finally turned against that means tested bare minimum, and the dems dont understand it.

So they think the only reason Biden is losing is because they haven't educated voters on all the stuff Biden has done (looking at you, Some More News). Under that logic it wouldn't be smart to run someone other than biden - look at all the stuff he's done!

Every election they also triangulate their position to be whatever the republicans had last election - There's votes to be won there! At some point that moves them so far away from the leftist base that the dems gotten used to relying on and being to take for granted. At some point there isn't a logical argument for that leftist base for why they should vote for Dems instead of republicans. Biden ran on being the "harm reduction candidate" and that's not really visible. They used to have climate change to gesture towards, but we are now at the point where immediate action needs to be taken, but the Dems aren't willing. At that point it doesnt matter wether they "believe" in climate change or not, they've shown they do not care about it. Same goes for immigration policy and civil rights.
The Dems have gotten used to being able to ignore these sentiments, why would they change now? It is only now that the chickens are coming home to roost, why would we expect the Dems to be able to realise their predicament?