I was just talking about this with parents and kids at different schools. As others are suggesting, the problem appears to be that at many HS, the most advanced classes are mostly AP classes, so taking a lot of advanced classes means taking a lot of APs.
Our private HS does not work that way. It offers very few AP classes, but it does offer many advanced classes. Indeed, many classes it argues are more advanced than AP classes, but they are not specifically designed to prepare you for AP exams. And if you want to take an AP exam in that area, you may need to self-study, as they have not taught to the test curriculum. And they don’t encourage students to do that, because in their experience colleges do not expect our applications to have a long list of AP scores.
But that’s because our private HS is well-known among selective colleges, with regular placement in such colleges going back a long time. I strongly suspect other high schools without that sort of context have shifted toward their advanced classes being dominated by AP classes in part because that serves as a sort of standardization that can help their applicants clearly communicate the difficulty of their courses to college admissions officers.
And although I am not sure that is ideal for the kids, it is worth noting that is pretty much how most of the world does this–sorta. Like, undergraduate admissions in most of the world involves taking several advanced courses and associated more or less standardized exams–A-levels in the UK and the equivalent in many countries, IB higher levels in many other countries, and so on.
But the thing is, admissions is then very course-specific. So, admissions will typically be based on something like 3 to 5 of these qualifications, and specifically ones relevant to your course.
Like, Oxford Biology admissions requires what they call an A-starAA for A-level applicants, with the A-star in science or math, and one of which has to be Biology and another Chemistry, Physics, or Math. Oxford also lets you satisfy those with IB higher levels of 6 or 7 (plus a certain overall IB score).
Then from the US, Oxford says you can meet the A-starAA with either four AP 5 grades (including required subjects, so you would need Biology to be one of those, and another Chemistry, Physics, or Math, and they have further requirements like that Math should be Calculus BC if available, but AB is OK if BC isn’t an option). OR you can do three APs at 5 plus a 32+ on the ACT or 1470+ on the SAT.
I am pointing this all out because while advanced courses leading to standardized tests is normal in most of the world, what is not normal is thinking you need to take like 12 of these advanced/higher-levels. Indeed, if 3 or 4 relevant APs is enough for Oxford, one might suggest taking a lot more is excessive. Of course since you can only take one course in most of the world (as in if you are admitted to Oxford Biology, that is your course), it makes no sense for them to require more.
But even in the US, although you can take a while to decide, you will only end up with a degree in some particular major (or maybe major and minor). So college-level studies in a gazillion fields in HS being normalized definitely seems not particularly ideal.
But again, I think what is happening here is basically highly-selective colleges are looking for students who do well in a diversity of advanced courses, and HSs in the US are essentially borrowing the AP system as a way of proving course quality to these colleges. And here we are.