I think it was a correct move from them.
Biden was not going to win, not a chance.
Whereas Kamala has a chance to win, I think it actually changed the entire "feeling" of the election.
Before I think Trump was the favorite, now I don't think he's going to win.
That's literally what the polls and odds are saying as well. Don't care what Republicans tell to themselves, they can keep believing what they want to believe, Trump is not going around enough at all, and Kamala is stepping foot to every important swing state, which is helping and right now Kamala is seen as the highest chance to win.
That is not just some wrong polls, you can buy polls, if I want to, I can pay a million dollars to these companies and make them show Kamala is leading or Trump is leading. But bookies are not like that, they know what they are doing, because if they are wrong then they lose money, so they will show the right odds and that's why I think Kamala is leading right now, that's the important part.
Trump may even withdraw, he has been going around saying Biden should take his candidacy back, think about how desperate he must be feeling that he already knows he can't win against Kamala, hence his point is not that he is better than Kamala, but his point is that Biden should take his nomination back.
This proves enough that we are talking about a person who already accepted defeat, and he knows it as well as we know it too and if he doesn't do something about it, he will lose.