The Fundamental Principle of Elementary Math Ed.
The math ed establishment does not understand the math behind elementary math.
Thus they are unable to teach it using concepts. This doesn’t matter if they call it rote learning, discovery, progressive or whatever. The math ed establishment doesn’t understand the concepts behind elementary math, so they can’t teach it.
The math ed establishment’s know-how is so limited, and their general apathy so great, that they can’t even recognize when new materials are made available to teach them the math behind elementary math.
Apathy over unteachable diversity does not fully explain this. There is enough teachable non-diversity for math ed to be interested in the math behind math ed. So some other explanation of their apathy and disinterest has to be found.
Part of this is they actually expect math to be about them. They think math is there to make them feel good and feel important. Approaching math with this attitude is likely to fail, and it does.