Why is anyone surprised by this? The ONLY goal in 2020 was to remove Trump. They didn’t care who replaced him. So they put up a senile old career politician and it worked.
Nothing else explains why there were SO many candidates running FOR the nomination. The DNC knew Joe was a mess, so they had to prop up as many contenders as possible against him. They would all run interference for the DNC. That way, the media would never spend too much time focusing or Joe's obvious flaws and failings