Re: Why would anybody care?
Read this (linked to above) https://blogs.msdn.microsoft.com/oldnewthing/20040525-00/?p=39193 and think again.
Writing a calculator app isn't too difficult when someone has already done the back end work for you. It's a tad more tricky when they have not.
For DirectX under Linux there is already DXVK, and other alternatives. Few people have an interest in DirectX integrated into Unix, when there's already Vulkan and OpenGL.
There's a lot more than just DirectX involved in porting games to Linux. It also doesn't help that despite a lot of work by Valve and others, Linux Steam usage is still under 1% and going down relative to the increasing user population.