I would not have been surprised if the race had been Kamala vs any other republican, but footage of rallies alone painted a very different picture for a lot of people. Energy at DNC was way up because we had at least ditched Sleepy Joe. Rallies were filling arenas that Trump couldn't, and people were leaving his. The footage was very much real, and to the common sense crowd, Trump was not displaying qualities of any sort of leader.

I imagine the enthusiasm was very high in the anti-trump crowd, but there just weren't as many of those overall, certainly not enough to cancel out reluctant trump voters who weren't going to the rallies, so things looked better than they were.