Usually it's "You can only use CoPilot"

Ya Microsoft lobbies for that, at our place too.

The reason is that copilot resells other people's models (they're just a middle man) and there's an easy way to cut them out. So they blow up the dangers of other people's AI. Whereas if your data is in M365 they have it all anyway whether you use copilot or not.

So that people don't feed proprietary data into a model that will train itself from it. Standard DLP practice.