The main problem with Linux as a platform, is that it isn't. Linux is a kernel, with a platform built on top of it. And that's the real issue: Gnome and KDE are separate platforms; but so are Ubuntu and Fedora; but so are Flatpak and Snap; etc. Depending on your application, you will have to support several combinations.
For gaming, Steam OS fixes that. You can't target "Linux", but you can target Steam on Linux.
Which is fine, its a much better situation than the current status quo,
If all devs build around steam OS's 'platform' its not that big of a deal for any Linux enthusiast to run in their custom made setup, the main concern is the layman, the enthusiast love these types of problems.
PS: I know its custom Arch Linux under the hood, I'm talking about mass market nomenclature.