The defenders of the existing system love mathematics because it is easy to test and there can be test prep courses and state-wide tests and national tests and tests comparing us to other countries, all signifying nothing.
Focusing on math is a tell that someone's innovation is of limited value in education. It is the discipline we've most simplified. Even if you can increase test scores in math (which is by no means a given), even raising standardized tests in other areas are a qualitatively different problem (let alone increasing the full range of educational outcomes).
This extends to general techniques like benchmarking standards and No Excuses charter schools.