Many of those “Steam Deck killers” market themselves that they use Windows to have better game compatibility though, average casual users don’t notice the different on Windows and on Linux. Also it seems like currently only Valve is the only one being interested on Linux gaming and taking serious, if any measure to improve Linux gaming. Even GOG with their anti-DRM stance (which may align more to Linux users) and Epic Game Store with their anti-monopoly stance (which also align with many Linux users too) haven’t done anything to improve Linux gaming or even port their store/launcher to Linux, and many manufacturers and machines don’t support Linux adequately or maybe even not at all (especially gaming machines). So it wouldn’t be so surprising though