I know what آپ mean. My highschool has only a few mainly Bleach and Naruto. I do know that in Middleschool it was because some of the manga has bad content (the whole blood, violence, gore, and smutty crap) so most of the کتابیں have to be review before being entered in.
Considering I assume the fact that لائبریری کتابیں come from the schools funding I don't think they buy them with it..they just buy regular book mine probably does it to enforce reading regular books..rather than manga..why I don't know.