I think one of the major causes of these issues is political.

In short, politicians want to "solve" education, but they also want to get re-elected. So they want to come up with plans that will have a confirmable success within one political term.

Real systematic changes to education can't be done in four years, but a tweak to standardized testing requirements can. So they add another test, or another level of testing, or a new target, or updated quotas, hoping that in a few years that can show that test scores are up, or something equally simplistic.

Once they start spending time doing that, they stop spending time actually trying to improve the system. The teachers have to teach for the test, so the students have to study based on the test, and there's no time to actually work with them to make sure they understand the topics.

Testing real understanding is hard.