Not mandatory by law perhaps, but how much power did e.g. a single teacher that wanted to teach Blender have to go around this policy? If almost every school uses the same firewall, and only software with lobbyists behind it gets whitelisted, that can be just as effective at suppressing free software as banning the teaching of Blender by law.

Even more effective, actually. A law is out in the open, plainly stating its function, easy to point to and vote to change it. But this kind of amorphous, corrupt, entrenched bureaucracy is much harder to uproot, or even identify.