They are spending it. On average they spend about 5% of it per year. In 2023 that was $975 million. It goes 53% to instruction, 22% to health care, 15% to student aid, and 10% to research, academic support, and other services.

The point of an endowment is to provide long term support for whatever the purpose is of that endowment. That is done by investing it and using the investment earnings for that purpose.