Maybe:
1) They initially had it as some kind of virtual classroom feature, but then an administrator or somebody decided it should happen without having to manually allow the connection and then they started thinking it would be entertaining for the teachers to watch?
2) They wanted to have remote testing and wanted to watch students surreptitiously to make sure they didn't cheat (because if they knew about it, it's really easy to get around)? And then they abused the system?
3) They want to uphold the honor and propriety of the school by monitoring student activities?
4) Some kind of sociological experiment?
I'm guessing 2, maybe a little of 3 is the most likely. If the administration allowed it, it presumably had some form of school-related purpose, as ill-advised as it was.