Let's assume CDPR were smart enough to avoid costly lock-in, so they are using Vulkan and etc. and etc. to make sure they are portable. I.e. with good engine design, costs of porting are not big. (May be they don't, we don't have the info, but nothing should have stopped them at least, like other developers demonstrate). Likelihood of better cross platform tools like Vulkan used also gets higher, when they are considering Stadia release (which runs on Linux and also requires using Vulkan).
And support costs actually go both ways. I.e. cross platform coverage exposes flaws in the code, fixing which benefits all platforms, in result increasing the quality of the product. So it's a good thing, not a bad one. For bigger studios especially it's a major plus. It's for smaller ones that don't have big codebase this benefit is not as important.