Correct me If I'm wrong, but the school hasn't actually been dropped - only radically changed/simplified and renamed.
Reason for the change? I think the lack of brothers has a big part to play in it. Because school assignments will now be in the form of preaching presentations and not instructional talks teaching the congregation, it means that a presentation given to a brother can easily be substituted by a sister. So a shortage of males in a congregation poses less of a problem in terms of finding a substitute.
Another reason for the change - or at least the timing of it - is to serve as a consoling distraction to some of the negative news swirling around Watchtower at present re poor handling of child abuse and financial difficulties. They have to keep up appearances that the chariot is still move ahead full speed, and thus the org. still has Jehovah's blessing even though they're actually mired in problems.
"Pay no attention to the turmoil at Bethel! Look at the shiny new meeting arrangements we've prepared for you."