It could only be because school administrators were won-over by the engaging user-experience - completely overlooking practicalities - back in 2010 even into 2014 iOS lacked decent enterprise-management tools that would enable staff to lock devices down as they're obvious distraction devices - things are made worse by Apple's decision to not have multiple user-profiles on the iPad and confusion with how Apple IDs work. I understand they've gone some way to address those issues - but other concerns still apply, such as the vision of a wide range of high-quality (and interactive, no-less!) iBooks to replace textbooks - simply hasn't happened due to massive cost of authoring even a single iBook. But the main blocker I feel is that staff (both teachers and school district IT folks) just don't want to have to manage them. I know an IT contractor who resigned his job at a private school after having to deal with setting up hundreds of iPad Mini devices for every student - he just simply hated the work involved.
As Apple is neglecting the desktop market, they're just as well neglecting the education market: remember when Apple had massive education market penetration in the late-1980s? Now there's not even an equivalent of the old eMac unless you count the now 3-years-old Mac Mini models.