Some of it comes down to insufficient grounding in math education preparation. In Illinois at least, K5 teachers are required to take a class that's effectively

Some of it comes down to insufficient grounding in math education preparation. In Illinois at least, K5 teachers are required to take a class that's effectively high school algebra, but at least where I got my credential, the class was taught as if it were just a remedial math class (which, to be honest, it was for more than a few of these would-be K5 teachers), rather than making it clear that the math that they would be teaching would be preparatory for the later class. Similar situations occur with 6-12 mathematics education preparation. This continues well into 200-level and even 300-level college mathematics. Gallian's Contemporary Abstract Algebra spends a lot of time exploring groups of the form a + b√n without explaining why. In general, it seems like math education should step back and read John Dewey and stop teaching mathematics as inert knowledge.