

Because DirectX is more than a graphics API.
https://en.m.wikipedia.org/wiki/DirectX
A fair amount of what used to make DirectX an everything API has been deprecated, but if you are already using Windows stuff for networking and audio, then you may as well use the graphics APIs too.
Not even in the slightest. Metallica went far above and beyond everyone else hunting down little old ladies to sue.
99% of bands didn’t make money from album sales, which is what makes all the hand wrangling over Spotify funny. Musicians idolise a world that never really existed.