I was under the impression that he was supposed to be handing off the role to Kamala, which was meant to be a shift towards a young(er) leader, woman and person of color that they hoped would check enough boxes for younger voters to make them think she was an actual progressive. That plan seems to have been nixed once they realized she has so little appeal across the board, she could probably lose a popularity contest to any number of infectious diseases, and Kamala 2024 got scrubbed.
They potentially could have found other viable alternatives, but they would have represented an actual shift in party leadership rather than bowing down to the party orthodoxy, so the DNC would never actually support them.
What they really want is another candidate like Obama that is charismatic and can talk in a way that convinces voters who don't feel represented by the current Democratic party to say, "This is the candidate who can deliver on reshaping the party in line with my views," while having no intentions of meaningfully deviating from the party line. I think the experience with Obama is still fresh enough in the minds of these voters that they are on guard against the same sort of deception a second time.
That it only becomes a topic of popular discussion once every two years doesn't mean people are sitting on their hands the rest of the time. I've volunteered on local, state and Congressional campaigns, mostly translating campaign website and literature/fliers into Spanish. I've done this in the lead up to the 2020 presidential elections, state assembly, city council and mayoral races here. If I talk to people about this stuff outside explicitly political gatherings or a presidential election cycle, I'm an annoying leftist who won't shut up about politics. When the rest of the country gets off their collective ass and pretends to care, I get "Why haven't you done anything in between election cycles, you're not serious," from the same people who didn't want to hear about local elections the last few years.
Yeah, it's pretty exhausting having the same liberals disengage between presidential elections and then pretend to be the arbiters of serious politicking once every 4 years to try and punch left and exclude any actual leftist viewpoints. Thanks for doing your part to keep that liberal tradition going strong.