Yes, thats how Open Source works or they can keep paying Windows. Asus knows their hardware much better than Valve does and has a much bigger interest in a good user experience, but currently lacks the incentive, because Windows is a „good“ paid alternative. Honestly I don’t understand all the downvotes.
Okay, understood. May be SteamOS was the incorrect wording. I meant the Linux Kernel, Arch, Proton. I am assuming most changes are related to hardware and software compatibility which should all be open source.