Valve have been removing a lot of Linux games from Steam which do not work perfectly on SteamOS, which while partially true is most certainly not the case.
In a conversation with a Starbound developer on Reddit, a Valve Employee has confirmed that the affected games are still available for purchase and download for Linux, but the SteamOS logo has been removed from games which require more than just the Steam Runtime to function, as these game are not certain to run across multiple varying Linux distributions.
We’ve been removing the store bit from games that cannot run against just the Steam Runtime, without additional dependencies on the host system. Games that fail this are impossible to support reliably across multiple distributions, and will not be publicly advertised on the Store as supporting Linux going forward.
All concerned games are still purchasable, installable and playable on Linux.
This move is clearly to force developers to implement more broad Linux compatibility and ensure that Linux games are compatible with Valve’s SteamOS. Hopefully gaming on Linux will continue to improve in the future, especially across multiple distributions of Linux as right now the reliability of Linux gaming is a real sticking point for gamers, especially when it comes to GPU Drivers.