No, they do not have 'multi-hundred billion dollar endowments'. Harvard's is around $40 billion, which is a lot, but income from the endowment only covers about a third of operating costs. It is all already budgeted for other purposes. Even for Harvard and MIT, $800 million is a non-trivial amount of money.
It's a shame how academy ends up being unaccessible for many people, even though they receive a lot of endowments... while there are a lot of ways to make them more accessible!
Like: online courses... or... What about the white elephant in the room? The cost of social events and Ivy League athletes/sports.
I don't have anything against those, but if I were in a position of power in one academic entity, I'd definitely make sure sports is not a cost center, as it is today for many.
I think you either misread what I wrote. The relevance is the that such activities have been driving up the tuition costs, so attending or not, they've a cost on the student.
Usually this extra cost is not explicit, though, as nowadays most students have to get a loan to attend university. This wasn't always the case.