I'm sure they've filled those 60 slots already, but within those 60, I'm sure there are people who have been accepted to other schools as well and won't be attending UCSD. SF is SD's main competitor for students, so as soon as students have confirmed their acceptances to SF (or another school), then SD can start pulling people off the wait list. But as the letter states, the deadline for students who have been accepted to both SF and SD is April 8th, so people on the wait list might not hear back until after that. I'm sure the wait list is not that long since SD knows that they won't have trouble filling up their class, so we have to stay positive.