I agree, I believe that they are mad that their campaign worked too well, they didn't want him to drop out as he was a viable candidate to win against as he was slipping hardcore poll wise and was shooting himself in the foot, he wouldn't have won. Now they need to re-evaluate their strategy to fight against Harris, which is going to be difficult considering that she is basically a counter opposite of what Biden was and has the exact opposite tactics he did, including background and has a solid history. I personally don't care much about her but, I can see where the threat is.
It also takes away the focus from his little ear booboo. Everyone will be focused on the Dems for the next few weeks unless something more interesting happens.