- Most people don't need to learn calculus at all, and it's fine if the few weird students who do start when they get to college (maybe the advanced students can learn single-variable calculus in high school).
- For pure signaling reasons, taking calculus in high school has become very important for college admissions.
- In order to take calculus in high school, you need to at least take algebra I (and hopefully geometry) in middle school. Wealthier parents understand they are playing the college admissions game early on, so they make sure in elementary school that their kids will be able to get on the algebra track in middle school.
- Getting on the algebra track is thus the first really consequential part of the college admissions game, it happens much earlier than the rest, and takes real scheming by parents to make sure their young kids are prepared. [actually true]
- If you could just make this impossible, it will even the playing field in a huge way and knock down one of the biggest hurdles in college admissions for people from lower-SES backgrounds. [also probably true]
- The only downside is that students will no longer have time to cover calculus in high school, which doesn't matter anyway because it's only a small number of unusual people who need to learn calculus (very advanced math!), and they can just learn it in college.
This is my best guess about the line of thinking that motivates these "no advanced math" policies. It has elements of truth to it which are worth paying attention to. The problem is just that actually, it's really useful and important to learn calculus in high school, and more people need this opportunity.
edit: I thought it was clear that I think a lot more high school students should be learning calculus as early as possible, and that "no advanced math" is a terrible policy, but I guess not...