> High school math is not a rapidly changing field

Are you sure? Here is a list of 16,000+ papers written about teaching high school math since 2018: https://scholar.google.com/scholar?as_ylo=2018&q=pedagogy+up...

Also, as a teacher, you have to adopt the district standards, which change every few years. Certain areas are removed, others added, some things are more important, some less. Those standards are changing to meet new standardized testing requirements.

There is a lot of change happening. Just like in programming. People who learned Cobol still need to learn new languages once in a while, because things change, even though the principles stay the same. It's the same data structures, same algorithms, but yet software engineering is rapidly changing.