Because he hasn't been the President for some time. And Kamala who has done basically nothing, is suddenly all over the place like she is the President already. These are all puppets.
They picked Kamala because she will do whatever she is told. Same reason they picked Biden. It's the biggest problem with our system. It's set up so that these puppets are hand picked who can easily be controlled. Well that and they are picked for demographic purposes, failing at the black vote? Get a black candidate. Failing with the women's vote? Gets a female candidate. Their policies don't matter, their policies will be what we tell them to be. Who ever runs the Democratic party is the real President. Kamala/Biden is just a face and a demographic.
It's why some people find Trump refreshing. He is anything but a hand picked candidate by the Republican Party. By appearance at least he looks like a wild card that can't be controlled by others. (I think he can be manipulated though, which is slightly different)