Looks like just the limit of tickets.
Not tickets; anyone can get one, no limits. It’s who shows up. If it’s not regulations, the campaign will have to spin this somehow. Sorry to see this, but it can be a combination of weather, covid-19 worries and violence and protest threats.
I also see this as the first test of the campaign seeing what it’s going to look like and what’s it going to take to do rallies in the coming months, especially in those battle ground states with Dem governors who will put all types of restrictions on the rallies.