So that it too can belong on the list of game engines that have supported OpenGL (Linux) for a long time. Unreal Engine, Id Tech, GameByro, and many others have been around forever with OpenGL and Linux support, and yet you don't see any games being released for that platform. I find it sad that it takes the lucrative mobile market to convince these companies to support anything else besides DirectX.
The worst part is, because these engines abstract from what rendering API they use, the studio using them for their next title shouldn't have to care about whether it uses OpenGL or DirectX for rendering and yet the fact that "Engine X uses DirectX YZ features" is always the main selling point of it with OpenGL support falling into the background.
Don't forget that AMD/Nvidia currently only produce hardware primarily for the desktop and consoles. Until many high profile games are ported to desktop Linux (not just mobile platforms) I don't think AMD/Nvidia will care about OpenGL any more than they do now.
You can look at
http://www.amd.com/report to get an idea. If you did find an OpenGL specific bug (let alone on Linux) you will have a hard time providing any information using that form because it is obviously tailored primarily to gaming on Windows... using DirectX... I've seen reports of known OpenGL bugs on their support forums only to get replied to and never visited again, even months later.