That's an entirely different situation voters would be responding to, and they would only be doing it because they would have no other option. Even then, it 100% would end up being Kamala Harris and a running mate they scramble to find, only because they need the name recognition. Those are totally different circumstances, extremely obvious and avoidable, but still technically not under their direct control like the entire cycle up to now.
What we have now is the party's unwillingness to accept that Biden needed to be told not to run again, so we could get a real primary and voters actually deciding. They are only now starting to question the shitty decision when it's becoming glaringly obvious that an 80+ year old shouldn't be running again and younger blood is needed.
The party is run by the old fucks though, and they don't want to give up what they have to the younger generations. Look at AOC's seat, it's the perfect encapsulation of the DNC's belief that the old fucks should be running everything.
AOC handily beat Joseph Crowley in the primary with 57% of the vote (against the #3 Dem at the time, a 20 year Congressional veteran, it's unprecedented), and he still refused to drop out. Instead he stayed on the ballot under a third party where he again lost, with only 7% of the vote. 7% despite being the "safe" politician, with 20 years experience, #3 in the party, the incumbent with all the name recognition in the world, being challenged by an upstart young female "bartender". The old fucks don't want to give it up, and will do anything to prevent that, even losing the election entirely to the Republicans, because they aren't doing it for the country, they're running for themselves.