There's this whole concept of "Embrace, Extend Extinguish", that a lot of people in the open source community hasn't forgotten about, and therefore find it hard to trust anything that Microsoft is about.

Microsoft is not your friend. Like most large companies, it tries to game the system to the detriment of the general public: Monopolistic practices (embrace-extend-extinguish, discounts for hardware vendors that only bundle Windows, ...), lobbying for software patents, tax avoidance, all that jazz.

There are also concerns with regard to civil liberties such as spying on their customers out of self-interest and on behalf of the US government, cooperating with authoritarian regimes such as China or their participation in Trusted Computing. Also note that while nowadays, just like many other tech companies, Microsoft might get criticized as being 'woke' by people with a certain political outlook, in the late 2000s, they were throwing people off xbox live for mentioning being gay in their profiles (or just having the surname 'Gaywood', for that matter).