I think there are several reasons Biden’s handlers keep him in a mask:
1) The Democrat base and the left in general love masks and want to see him wearing one.
2) They don’t want him to get ahead of the blue areas that still have outdoor mask mandates in place. He’ll keep wearing the mask until places like San Francisco have dropped their mandates.
3) The left wants to maintain an air of crisis because it helps their agenda. The mask communicates crisis and un-normalcy.
4) It appeals disproportionately to women and minorities.
5) It’s the opposite of what Trump would do, and they want the contrast.
“Crisis is the cry of the tyrant.”