[Fomite]

This phenomenon (which is just an extreme version of out-of-state tuition for state schools) is almost entirely undergraduate driven, not STEM PhDs, who as mentioned in other posts, have tuition either waived or paid for via grants.

There was a whole thing if you recall in the first Trump admin about treating tuition waivers as income, which at an Ivy is potentially a financially catastrophic thing for a grad student.