malikhis: I do agree there is no good reason to be using DirectX these days, but microsoft has the money to take freedom away from the consumer. They did after all pay for GPU companies to butcher their OpenGL drivers.
Luckily that is now no longer a real issue as there's Vulkan, which is fully supported on Windows, the successor of OpenGL and way more modern and performant (e.g. fully supporting multi-threaded rendering, which OpenGL doesn't). One could argue Apple is doing worse stuff today with only supporting Metal, but since this API is almost identical to Vulkan, there's MetalVK to add a small compatibility layer on your Vulkan engine.
Still, if a game runs perfectly fine in vanilla Wine (+ dxvk if it uses DirectX for rendering), it's good enough for me. It's really to compile & test such a big game on more than one platform, so it's not just the one-time porting costs, but ongoing expenses for additional development & QA time.
I'd more importantly want to have GOG Galaxy for Linux, as it's running poorly/crashing with Wine or Proton, but since it's based on cross-platform libraries (Qt, CEF, Poco, Python etc.), it should not be THAT hard to build a Linux release. Then add support for Proton (there's no restriction on using it outside Steam) and done.