The XBox was named after a Microsoft API. Definitely one of the more clever ways to force developers to eat your dogfood.

When it was created DirectX was a really useful thing for game makers. It made it easier to write hardware accelerated applications that were also consumer friendly. Contemporary Windows is full of anti-patterns. MSFT just can't seem to resist sticking things into it that make it less pleasant to use in support of MSFT's ecosystem. It's no wonder Valve invests into trying to be independent of that.