The DNC keeps Biden because he is a useful puppet. He will do exactly what he is told.
Yup! This.
They probably cannot be any happier with this candidate.
If he wins, they’ll be able to do whatever their satanic hearts desire.
Usually, a politician has to go through a lot of heat and hard effort to become president. This can make them strong willed. Having a complete puppet is a long held wish for the manipulator behind the screen operatives.