Because they boxed themselves in with legalese. Companies would definitely switch off Microsoft services if at all possible if the company's lawyers thought their trade secrets were getting sold off. So I think the "as necessary" framing does probably prevent them from doing some things.

As I laid out in my other comment, I think training AI in particular is covered under the "improving Microsoft products or services" bit of legalese. I do wonder how companies lawyers will respond to this though. They probably thought of that phrase as just allowing Microsoft employees access to documents to see how Word or other pieces of software were being used, or to fix crashes, etc.