Endowments need to be taxed out of existence.
1.) thin air
2.) the government (??? No.)
3.) higher tuition -> hint: pick this option!
The better question is why Harvard and Princeton charge tuition at all! (The answer to that question is not that hard either.)
Wealth redistribution / market segmentation.
Princeton has quite large aid packages outlined here: https://admission.princeton.edu/cost-aid
Harvard has different but also quite amazingly large aid packages for lower and middle-income students: https://college.harvard.edu/admissions/why-harvard/affordabi...