I’m not sure about whether it HAS to be this way, but . . .
I think it is often illuminating to look at the operating budgets of these schools, and see where their money for operations actually comes from.
At a high level, holding aside when hospitals are involved (which is a whole other thing), the main sources for operating funds are research grants, state grants, net tuition, gifts (either for immediate use, or filtered through endowments), and returns from other operations (university presses, various fee-charging services, and so on).
Private colleges obviously don’t get state grants, but then private colleges also vary among the remaining four main categories.
And for MIT, their top sources of operating revenue breaks down roughly like this:
Research grants: 46%
Returns from other operations: 24%
Gifts: 11%
Net tuition: 9%
For Harvard, it breaks down roughly like this:
Gifts: 45%
Net tuition: 21%
Research grants: 17%
Returns from other operations: 17%
OK, that’s pretty different. From poking around budgets, it is also pretty typical. As a top “tech” college, MIT gets WAAAAAAY more of its funding from research grants, and really that extra 7% in returns from other operations is mostly tech-related too.
In contrast, Harvard gets WAAAAAAY more of its funding from gifts, and also a lot more in net tuition too.
And to be very blunt, this explains a lot about their admissions practices. In fact, when Harvard was confronted with a choice of explaining their admissions practices as either a result of ethnic bias or something else, it chose something else, and then in part explained a lot of what was going on is that Harvard is trying to manage its long-term financial plans, including how it planned for its endowment and other gifts to continue supporting its operations for generations into the future.
Now, there is some empirical debate about whether Harvard and its peers are getting this right. Like, some people have suggested things like legacy policies don’t seem to have important gift effects. Some have countered that these studies are not looking at multi-generational time scales.
But at least Harvard seems to believe its admissions policies are ultimately informed in part by the need for future gifts. And then of course needing a lot more net tuition to balance their budget is pretty straightforward.