I suspect that part of the problem is that many teachers, and also students and parents, even before gender was an issue, were being heavily pushed along other identity politics lines around race, sexuality, etc. But not in the same way as many of us who are older would remember from school.
What I find really noticeable now when I am in schools is that all of these ideas are simply taught as unquestionable truths, that there is one way, for example, to think about race, or sexism, or sexuality, that is right. And people who disagree, or did so in the past, simply did so because they were racists. Now, we know better so we do better.
There is no sense among even the older children that it is possible to have an intelligent discussion about some of these questions, that even among non-racists or people who aren't sexists there might be differences of opinion on certain issues.
So when gender ideology came along, it was slotted into the same kind of approach. Teachers treat it the same way, and many would see questioning it the same way they would see questioning the latest antiracism idea - as something only a bigot would do.