Valve has reportedly been removing a number of Linux games which don’t meet their quality control requirements or suffer from compatibility problems on SteamOS. According to Gaming on Linux, the SteamOS icon was removed from titles including Ticket to Ride, Anodyne, Lume, WAKFU, Starbound, Evoland, Oniken, StarMade and Defender’s Quest: Valley of the Forgotten.
The developer of StarMade suggested this was due to the game requiring Java and should be rectified soon:
@gamingonlinux It is because the game requires Java. When the new launcher comes out this should be resolved!
— StarMade (@star_made) October 17, 2015
Although, other developers are completely unsure why the SteamOS icon has been removed. Possibly, Valve is testing each Linux game for features such as full-screen support and only approving those it deems acceptable. This could be a positive step to add polish to Linux games and make the end-user know every approved game is fully functional. On Windows, many of the older games struggle to work, yet Steam still sells them without any qualms.
To clarify, Valve are not removing games without the SteamOS logo from your library, but it’s certainly an unusual development. Gaming on Linux is a niche outlet but there is a lot of potential if the Vulkan API manages to outperform DirectX 12. The popularity of Windows 10 doesn’t make it seem likely though.
Have you tried SteamOS?