I think multiple things.
* They believe they are in the lead.
* They have their media surrogates working day and night.
* They are hoping Trump implodes or continues to speak off message.
* Their policy ideas are radical or they are trying to deceive voters so they remain non committal.
* They are trying to find ways to cheat as much as possible.
* Joe is a weak candidate and is a risk the more he is in public.
* Kamala is a weak choice for VP but they like racial politics.
* There is no demand to hear one of their rallys.