You also have some groups on the left attempting to promote the idea that math is racist

That seems like a much more recent and much smaller phenomenon. The censorship and attempted or succesful modification of school curricula (esp. evolution/biology and sex education) by 'right wing' christian groups goes back many decades across much of the southern US.

>smaller

Didn't some states remove math requirements for highschool graduation?

There are plenty of south/East Asian counties that have just as much if not more restrictions in textbooks. So I don’t think that alone accounts for the discrepancy

Be careful about reading and comprehending schoolbooks in Texas. Parents don't like to be pressed on most of the content, and are sometimes going to great lengths to get your book banned entirely.

That story wouldn’t work in deeply secular England, & it seems unlikely to explain underperformance in maths.