It was not some grand plan, it was a massive failure.

[Metaphorical]

73. There were several key extenuating circumstances here

1. I think there were very few people on our side that wanted Biden to drop out for ulterior reasons, but enough people who came into regular contact with him were uneasy about his growing frailness and the more consistent senior moments. I remember seeing him in an interview with the UK Labour PM, and he looked frail then.
2. I think that Biden did not want to make a decision until after the RNC Convention. Note that his decision was not to resign the presidency, but rather to drop out of the race. This was a hard decision, but I think the main concern was that he didn't have the energy to consistently both BE president and RUN FOR president.
3. Also keep in mind that he wanted Trump to commit to a platform, and there was a lot of hope that Vance would be the VP nominee. This meant that Biden had to keep the possibility that he would continue to run in Trump's mind. (I have no doubt that Biden's strategic sense is still finely tuned).

Could they have handled it better? Arguably, yes, especially at the Democratic leadership level, and no, this outcome is far from ideal, but that's politics.