Here's one I have raised myself:
Neither political party, at the leadership level, really wants to fix the education system. It is too easy of a political football for both sides to use to leverage their bases, as well as use as a door to push policy through that impacts other areas of society. You actually do something to really fix problems, or address the root issues, you risk angering your voting base, or losing that wedge issue through which you squeeze through your "reforms" that have little to do with educating kids.
Of course, I'm just a crazy social studies teacher, so I could be wrong.