The Muss gets a certain allotment of seats for the games. Not all 32K students could show up to a game. Tickets are free, but you still have to get them.
When I was in school, you could walk right into the student section on game day and have a whole bleacher row to yourself, but basketball there were plenty of games you’d have to go early or even camp out for a ticket
I don’t know the exact number, but the student section is only around 6000, so that leaves 39K that are sold for every game with a long waiting list for season tickets.
Granted a lot of those seats go open at games, but they are all sold.