I think that answers the question.
The way US News is currently doing things, if you do a really good job improving the prospects of the typical students who actually enroll at your college, you will get rewarded in their rankings. And obviously it is often easiest to most improve the prospects of students who do not come into college with all sorts of family advantages.
Whether that benefit would work out the same way for the many different sorts of students who choose to enroll at very different colleges across the country is then largely immaterial. What matters is that you are serving well the students who do choose your institution.
Whether rankings SHOULD work that way, indeed whether generic rankings make sense at all, is another question–but largely out of bounds.
As long as you understand the current US News rankings DO work that way–it makes sense out of a lot of what we are seeing with colleges like Merced.
Indeed, and that reflects the same sort of reality–in fact, lots of public universities really improve the life prospects of lots of their actual students. That is their core mission, at least in-state, and they are often doing it quite well.
Upward social mobility was not traditionally part of the core mission of many of the most famous private colleges and universities. Over time, though, some of these institutions adopted it at least as a secondary mission. But they are also operating very expensive colleges, and net tuition is usually still an important component of their operating budgets.
But still, they have budgets for need-based aid to make their colleges more affordable for at least some students, and in fact the more non-tuition-based financial resources they have, the more they can afford to do that.
So some of the most famous AND most wealthy private colleges have held up OK in the rankings shift. But some, often ones which are not quite as wealthy and still need quite a bit of net tuition to make their operating budget, have fallen harder.
︎1. Williams