Thanks—that was a great article. In the few weeks since it was published, Biden withdrew. Let's use Occam's Razor here.

Biden said he would consider withdrawing from the race if his doctors recommended it. Then he came down with COVID-19 and went into isolation. When he came out of isolation, he announced that he was withdrawing.

It looks to me like his doctors recommended withdrawing, so he did. He and his doctors probably did many of the things you suggest here.

No conspiracy theories necessary.