Yeah, in the greater scheme there is only a narrow slice of the US college-bound population that is full pay private/OOS.
But when you add a filter for colleges that are particularly popular among highly-credentialed kids (including very high standardized test scores, consistently high grades in college-level courses, high results in a variety of competitions for kids, highly individualized and superlative teacher recommendations, and so on), well, there is so much correlation between those credentials and family economic circumstances that this slice becomes a lot bigger.
Then highly-credentialed kids looking at those colleges are even more disproportionately represented in these forums, including because for many other purposes their HS counselors may well be all they need. Again, in the greater scheme, a lot of college admissions is not so hard to understand/predict, it is only when you are looking at these holistic review colleges that get many more highly-qualified applicants than they can possibly accept that the “need” for a lot of advice becomes readily apparent.
So yeah, I am not inherently suspect of highly-credential kids who come here looking for advice about these sorts of colleges, and who say they are full pay. That would be a lot less frequent in the greater world of college-bound kids, but among those kids looking at advice for those colleges, well, the slice gets rather big.
As an aside, though—I do think there is a rather large information gap when it comes to LESS obvious private or OSS options that might nonetheless work out really well for various kids, including but not limited to highly-credentialed kids, and not least kids with good credentials (not necessarily the best, but good) and who are on a budget that need aid alone might not meet.
Helping kids like that find some interesting non-obvious options to consider–including perhaps when their HS counselors are not really able to provide such help–seems to me like one of the most valuable things this community does in the Chance Me/Match Me context.