Try a thought experiment. Imagine you are Joe Biden and you are running for president. You go out to do campaign appearances and a handful of people show up. Meanwhile you've seen the President's rallies on TV and you know he draws thousands, often turn-away crowds.
I know your handlers say to criticize the Prez for allowing a large group to come together, but meanwhile how do you feel about your popularity versus the Presidents' evident popularity? The polls say you are the choice of a majority of voters, so why don't they show up for you, cheer for you, do boat parades for you?
I have to think at some level this demonstrated disparity in popularity has to be galling. He has to be telling himself that come Election Day he'll be vindicated and the Orange Man will be shamed. What does he tell himself if that proves not to be the case?
What if the crowd sizes are an accurate indicator of popularity? Pollsters who measure voter enthusiasm suggest they are just that. The polls blew it four years ago, who's to say they haven't done it again? I think if I were Joe Biden about now I'd be scared silly.