Through need based financial aid, these schools are very affordable for many of those students.
https://en.wikipedia.org/wiki/Household_income_in_the_United...
I assume GGP was posting the "at no cost" threshold and that doesn't mean that $125,001 in assets and you get no help.
It's been a long time since I appli d for financial aid, but I do recall that other kids in college (though perhaps not college-bound) was definitely a factor in financial aid calculations.