It isn't so much that parents aren't interested in the quality of the eduction, as much as the annoying fact that teenagers have wills of their own. You make it sound like the parents are the target customers for these schools, but based on how the schools target their advertising they realize that their target customers are very much the kids.

Now admittedly I don't have teenage kids, but from what I hear I imagine it is non-trivial to tell them that they can't go to the school they have their heart set on and instead must go to a school they don't want to go to at all. And even if the parent does win that particular battle of wills, I image that the kids motivation will have taken quite a beating. I suppose at the end of the day most parents reason that it's better to send their kids to a bad school they are enthusiastic about rather than a good school they don't want to go to.