I firmly believe that the small crowd was due almost solely to COVID-19 concerns. That may have been amplified by the expected crowd size, but in a non-pandemic world I don't think crowd size on its own would be that much of a turn-off (I'd expect it to have the opposite effect, in fact).
The bigger thing the kids did was wreck the Trump campaign's voter database. Parscale kinda gave the game away when he bragged about the "biggest data haul" ever. This was about getting contact info for targeting GOTV efforts in November, and now their database is full of garbage - fake names, fake email accounts, fake phone numbers, etc. Whether it was envisioned that way or not, this was a strategic blow as much as a tactical one.
So everybody's been putting soundtracks over Trump's dejected walk from Marine 1 back to the WH (of which "Everybody Hurts" is still the best), but my wife noticed something and I see it too - that's the most normal he's looked doing, well, anything. He's not tottering or otherwise acting enfeebled, he's standing up normally, his gait's fairly natural, hopped down the stairs from the chopper like a champ.
My wife's theory is that he has a real phobia about falling, and without a handrail or someone to hold on to his brain just goes into overdrive so even a slight 3 degree grade is like looking at a cliff.
We already know Trump is a giant ball of neuroses and phobias already, so it kinda fits. That, and we're reasonably certain he has lifts in his shoes which explains the way he stands like a centaur, and you know that has to play hell with his balance as well.