That’s something I think some people just missed when Biden dropping out was debated. Of course, the other potential picks were polling behind him at that point. But he was showing clear signs that he had peaked, and would only be able to fight not to drop further. His most powerful argument had been not being Trump - which any candidate can wield. And any candidate with charisma and the ability to speak, debate and campaign has a lot of room to move up, whereas Biden was fighting not to move down.