I think it’s a leverage thing, or a perceived leverage thing. In most cities, it probably would not take much for a few baalhabatim to get the school to open their books. But good luck getting it in Lakewood, where few people pay significant tuition and everybody lives in fear of not having a school.
In general, I think it’s a good idea for several reasons. It would cause the school to only incur justifiable expenses. It would assuage the people who wonder where all the money is going (again, more of a concern where tuition is $18k rather than $4500.) It does stand to reason that if people are not given a choice where the money goes, they at least have some way to know where it’s going. And perhaps some more enterprising parents could make useful suggestions to a school that is doing a poor job of budgeting, or volunteer more when they realize that the school really needs the help.