I lived in the Bay Area until 2019 and my kids went to school in Piedmont, which is one of the top funded school districts per capita in California. The math curriculum at Piedmont junior high-school was a joke. The math book was electronic-only on a crappy chrome book and the book had no lessons, only problems. The book seriously tried to introduce the concept of exponents, and so many others, into problems without explanation. Teaching my kids math became a 10 hour a week job for me and my wife. Piedmont HS lost their physics teacher to another school that paid better and didn't replace the teacher for the entire year; a whole year of HS students, some of them seniors, whose opportunity to take a good physics course was blown. My family moved to Colorado recently... partly because of the CA education system.
Back when I was in junior high and high-school in the late 80's and early 90's... math classes had hard-bound printed math books that actually had lessons and clear examples so that it was possible to learn math concepts, on your own, even if the teacher didn't know what they were doing. Whatever happened to good books?... it is not like the subject matter has changed in the past 20-30 years. I thought it is proven that students learn better from quality printed material, with appropriate use of color, over e-screens (correct me if I'm wrong) and yet all education is going to screens.
I had great teachers in HS; both my physics teacher and math teacher had masters degrees in their respective fields. Today, there is no good financial reason to be a teacher with a Physics, Math, or Engineering degree in most CA school districts and that is, I think, a big part of the problem. If you don't have good teachers who can present a topic well and engage a class-room then students aren't going to learn the topic and progression through mathematical curricula is going to fall.
Another factor is probably demographic. This is anecdotal but I switched high schools after my freshman year from a HS in a lower middle class area in Sacramento to a pretty wealthy, upper middle-class area in Southern California and the level of the average student was quite a bit higher. The teachers were probably better overall in the SoCal HS but I don't think the teachers were that much better. But there was huge cultural difference in the student body of the two schools. At the Sacramento HS, I took geometry as a freshman and there were a lot of juniors and seniors in the class. None of them were dumb people... it is just that doing well in math and the going to a good college was not something on the average student's mind in a poor community. At the SoCal HS, most students were very interested in doing well in school, took math and science semi-seriously, and looked towards going to best college they could get into. Almost every student at the SoCal HS at least took Trig/Pre-Calculus.
Bring this all to the topic at hand... this does feel like some Kurt Vonnegut stuff and I am really disappointed. Holding back math education in mainstream public schools is going to push more parents, who can afford the time/money [read: the more affluent], to put their kids in charter schools, private schools, or supplemental education for math [e.g. Kumon]. This going to limit opportunity for the less affluent and probably increase the gap in math education across economic dividing lines. This may also pull money away from public schools over time.