> I see no practical way MS could benefit from this other than by improving the open source project.

Then why don't they make it opt in?

> Is there actually a good reason to turn this off?

Security. In the sense of "enable only needed features, to reduce attack surface".

Of course it would be even better to not have it turned on by default in the first place.

Microsoft comes from a place of being automatically distrusted by a lot of people, and for good reason. It may seem unfair to you, but they have to conduct better than this to make up for this disadvantage.