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.
I always phrase it as the principles (mostly add/delete) stay the same, but the methods are almost always different. Once you learn the principle, it's always about the method of getting there.
That's still work though. You might know all you need to know on the subject you will teach, but if the standard you have to fulfill changed, that means you have to change your plans.
Most of this change is driven by something other than need. The high school mathematics curriculum is a bit of a funny beast in the US, but it is certainly not the weak point in the system.
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.