Several reasons firstly Universities arent mortal individuals that live a 80 to at most 110 years, these are institutions that many of which predate the countries they are in.

Secondly they are receiving endowments from many individuals and organizations on top of tuitions and cuts off the top of grants researcher working there receive.

Thirdly they arent just getting simple compound intrest from money setting in a savings account instead they run private equity funds and hedge funds, which are themselves morally suspect