They are pretty angry that asians are outperforming other groups, and the intention is to suppress the accomplishments of groups they feel are doing "too well", literally making Harrison Bergeron a real thing. In terms of calculus in high school being too overdone it's not too early at all for smart students. Many countries have a gymnasium style system and you can do much more than calculus in high school. In fact, this was even done in the U.S. in the past. Russia, Germany, France, and most Eastern European countries have math gymnasiums where you learn much more than calculus. The graduates of these are the ones that go on to be world changing mathematicians and scientists.

The problem is that the racial distribution of those students who are good at math upsets the blank slate world-view of the teachers, and the very notion that some students are smarter than others and that these discrepencies have consistent ethnic patterns fills them with a lot of rage due to their politics/religion. Trying to infuse the same dysfunctional beliefs into the math curriculum will serve to spread what crippled the teachers' analytical abilities to the students. That type of denial isn't going to help train engineers either. Bridges can't fall down, processors need to work, theorems require proofs. These are objective things that students need to master, not comfortable delusions about everyone having the same abilities in every subject.

So you can only deny reality for so long before you start losing your competitive edge and this affects your ability to be a leader in chip production. By suppressing opportunities for groups they don't like, the teachers are preventing students from achieving their potential. Wealthy parents will withdraw their students and either home school if they have the education to do it, or place them in private schools that try to maximize the potential of every student, regardless of whether those outcomes are racially balanced. But that's a minority, the middle class and poor will be denied a good education.

Taiwan and China are under no such illusions. They are happy to identify smart students and give them challenging topics in order to help them achieve their potential, rather than trying to slow down the best students in order to pretend that everyone has the same talent for math.