That is, until people start passing out in the summer months, some even during the early fall and late spring semesters. You can get a good workout inside an air conditioned building.
There were times last summer when I'd go to the rec to see a friend who was working there and get a thin layer of sweat just standing on the 3rd floor. Not everyone who works out there is a young, in-shape college student. I'd be willing to bet that during the summer the majority of the users are older faculty, staff, alumni, etc., who are trying to stay healthy and working out in 90+ degrees isn't good for them. Take a look at the thermometer on the desk in the 3rd floor sometime in the afternoon from about late June through late August. Very few times will it be below 85-90. Then add in humidity.