I assume the people who pressured Biden to drop out, simultaneously pressured him to endorse Harris.
I’m not an insider, so I am in no position to say exactly what happened.
But my assumption differs from your assumption. I do agree that Biden had his arm twisted to drop out. So he dropped out. And I believe as a way to stab his party in the back he said, “I’m dropping out -—— and I’m endorsing Kamala Harris as the nominee.”
It’s very hard for me to believe that the party wanted to get rid of Biden, with a chance to start fresh, AND would freely choose Kamala Harris as their very best option.
But I wasn’t there.