I think we’re all trying to be helpful. I have family overseas (and in the UK) who have spent time in the US for various reasons (post-doc, visiting professors, etc.) who assumed they’d need private school, and then were astonished to discover that the public schools in many (not all) “college towns” were fantastic. They didn’t know (or forgot) that much of our school system costs are paid locally, controlled locally, etc. So a university town which has faculty, staff, administrators living in it, are likely to be quite influential in deciding what gets paid for and why. These aren’t decisions made thousands of miles away in Washington- the tax base is local.
This isn’t every college or university town of course. But there may not be the need to budget in the tens of thousands of dollars required for private school if the local school system is strong. And someone living overseas may not realize that in a college/university town, there is a prevailing expectation that the kids are college bound. So it isn’t hard to access a solid college prep curriculum.