Chris

Because it’s an unwritten rule that a sitting president gets to decide whether he’s going for a second term. If he wants to do it, the party doesn’t defenestrate him. However, in this case Biden’s originally-stated intention to be a ‘transitional’ figure was set aside. Most likely, I suspect, at the urging of those close to him who were exercising a very significant amount of influence over him given his evident cognitive decline, and enjoying their taste of executive power. They will have told themselves they could keep making the decisions and as long as they could prop him up in front of a camera from time to time they could make it through another term.

It took them so long to make the change because those who were trying to keep Biden in the race needed to see there was no way he could win before they were willing to accept that their project was only going to result in Trump in the White House. Once they accepted that, they had to talk Biden back down. By the time all this was done it was almost too late.