They don't trust voters not to choose a succdem and offend pwecious widdle capital, and they're worried they couldn't fix a second election after 2020 almost went to Bernie despite their best efforts. So now they're just propping up the old man strategically until it's too late and they can put whatever blob priest into office they like without the unwashed masses messing it up with their "democratic will" or whatever. Technocrats must sit the eternal throne whether the people want it or not.
Synthesis: some of those clusters thought their chances were better if they skipped the primaries and waited to insert their person whenever Biden keels over.
(But I think they were largely caught off guard with how early he sunk.)