Few hours ago I had a short discussion via email with the principal that boils down to "we don't really want you to do any more lessons" with some of the least supported by evidence reasons I've seen this side of "we need to make more ice cubes to combat global warming".
You were donating your time to the school, and the principal wasn't professional enough to have a straight conversation with you? I'd venture the reasons aren't terribly important, because office politics are inane at the best of times.
The real question is,
I actually feel really, really, good in a role of lecturer.
do you want to find another outlet for that?