For someone who wasn't pushed out, it sure took him a long time (and a lot of political pressure from Pelosi, Schumer, the Press, etc.) to make that decision after declaring he was "All in".
Some people can be slow in realizing their own limitations sometimes.
As an example, I've needed glasses for distance for a while now, but I never needed them to read. But, after several times when I had to move my book a little further to see small text, my wife suggested I get a pair of reading glasses. "No," I said, "I don't need glasses to read." So I squinted, I moved the book further and further away, and struggled to read sometimes. I even tended to prefer books with larger text, when possible. But I refused to get a pair of reading glasses.
Then, one day, after failing to read the tiny text on a prescription bottle, the wife handed me her reading glasses and said to try it. It worked. So....I got a pair of reading glasses. The smallest magnification possible, granted, but they help.
The wife, she's a smart cookie.
Point being, Biden is 80, but he's more fit and more energetic than many other octogenarians. He probably figured he could do another 4 years, but it was only after being convinced by his colleagues, the press, and probably after seeing how he looked during the debate with Trump, that he finally realized he probably wasn't as up to the task as he thought. It was only then he realized he had no choice but to step down, and let his chosen running mate take over.
At least, that's how I figure it. Obviously, others see it as some kind of coup or something, but that's not even close to the definition of a coup...or reality, for that matter.
When he said he was "all in," I'm sure he was. It just took him some time to realize his limitations.
-- A2SG, unlike some people, who will obstinately deny they ever have any.....