Microsoft embraces open source because they found out that there are other methods to monetize and lock in customers. As a bonus people seem to like you when you give them stuff for free, even with the catch of privacy invasion.

In other words, they stopped copying Apple and switched their sights on Google.

The stuff that matters stays closed source. Infrastructure, tooling are published because they bring massive amounts of goodwill and developer mindshare while hindering potential competitors that now have to battle with a free offering.

Frankly I preferred the old Microsoft which wanted your money, not the new one that (also!) wants your data.