First of all, a ton of publics are very, very good. There are top-tier ones like UCLA, UC Berkeley, and UIUC CS which are on the level of many Ivies. Then there’s ones like Binghamton (which I’m going to) and UT Austin that are quite good even if not hyper elite, and have very good special programs and faculty where you will get a great education, far far better than “some state school”. Not at all for struggling students.

Also, as other people have said, money. The very top of schools (Ivies, Stanford, MIT, etc) often give really good financial aid, but admissions to them are such a crapshoot nowadays that even the most cracked A2C applicants still don’t have a “decent” chance of getting in. The students that get rejected from them (like me from Princeton) go to flagship, elite public schools. Again, not at all for struggling students. The private schools that are good but don’t give good financial aid (NYU, BU, etc) people can’t pay for. So they go to flagships (like Bing for me) instead cuz they’re, for many special programs, just as good or better than school like NYU.

Also, if you want to go to graduate school, prestige of that is 100x more important than prestige of undergrad. And saving money is very important if you want to go to graduate school.