If you look at the history of why public education in the U.S. was enacted, there were 3 main reasons, none of which were actually educating children:
1. Assimilate immigrant children into American culture so that they would think of themselves as "American" first and whatever ethnicity they came from second. (Hence, the Pledge of Allegiance, national anthem, American football games, focus on history & social studies in class, etc.)
2. Provide childcare during working hours so parents could go to work. (Hence, compulsory education, hours that aligned with a factory schedule, high student-teacher ratios, etc.)
3. Teach children the skills they would need to be successful in the factory system. (Hence, attendance, arriving punctually, moving between rooms at the bell, following orders, not complaining, etc.)
What's happened over the last 40 years is that the factory system in America fell apart, and so the skills needed for it no longer seem all that relevant compared to actually getting a good education, which school is not all that effective at. Meanwhile there are new waves of immigration with parents that were often highly educated (moreso than native-born Americans, oftentimes) abroad; they don't buy the "this is what a good education looks like" explanation, because they have had an actual good education abroad. And the Internet in general makes people much more suspicious of institutions, because you can see the ways that different power centers try to enforce control of the discourse, and there is no unified discourse to get behind anyway. The public school system in America is deeply embedded in the industrial institutions that were developed from 1900-1980, and as those institutions collapse, the public school system collapses with them.