I believe Biden was chosen in 2020 by the DNC to be the candidate, even though he was doing horrible in the polls, because he was the most malleable for Obama‘s third term.
Since it was so successful, they did not allow anybody to run against him in the primary. It’s also my understanding that the Biden ministration takes the position that zoom meetings are not records that need to be kept. If that is the case, there will never be any telling who’s been running the show.