Many people do. They also give money to improve football facilities, bring speakers to campus, and endow a chaired professor position.
> I don't donate to Wal-Mart, so why would I donate to University X?
Because a university is a nonprofit that exists only for the purpose of improving the world. (Not necessarily the employees, who work there as a job, but it's why universities exist.)
You probably don't see a lot of donations to the University of Phoenix or other for-profit universities.