Those asking "why?"
Going by all the teachers I know and have worked with for the last 13 years? Its probably just a case of him having copied his personal drive and the shared drive when he left each school, then dumped the lot on the new school's server.
A lot of teachers have a poor grasp of the idea of data security of copyright. The idea that the work they've done at a school doesn't belong to them and they have no entitlement to it is an alien concept. The idea that they need to be careful with data is similarly often an alien concept. They simply don't think about that.
Teachers suffer from a sort of tunnel vision - they only care about what specific thing they're doing at that time, and ignore everything else. So, he likely didn't even consider what he was doing when he did it.
Biting the hand that feeds IT
