I've been noodling the plausibility of the idea that Biden knew some time ago—days or maybe more than a week, who knows— that he's toast to the electorate and needs to pull out, but the party can't just take him off the ticket without any plan, so they are negotiating several things to make the transition seamless as possible, such as who's going to replace him (maybe not Kamala), what the ticket will look like, how certain top delegates can whip lesser delegates into line, how donors will react, things like that. They couldn't say out loud they're doing something like that because that would look even more chaotic than what we see looks. And Biden can't say he will pull out in such a scenario, so he continues to insist he is staying in the race, even as he understands he has to pull out, because that draws less fire than they are prepared to fight at this moment.
I have no evidence of this, and I'm not saying that's what's happening, or that I believe it is actually happening. I'm speculating on the plausibility of it, which I think is enough that it lies within the range of outcomes.