Why Are Democrats Running Biden?

My take:  Democrat movers and shakers "knew" Trump would win back before Covid. At the time, Biden served well as a placeholder.  It was Biden's turn and it shut out Sanders.  Then came Covid making a Democrat win possible because of unhappy voters.  The strategy shifted to hide  the increasingly senile Biden they were now saddled with and to amplify Covid dangers to keep voters unhappy and to keep Trump out of those monster rallies.