OpenGL isn't exactly a product. There's no company that "writes" the OpenGL software. Rather, it's a specification published by a consortium. "Writing" the OpenGL libraries is a task that each GPU maker does independently. So you have a bunch of different implementations of the same API.

For a long time, GPU makers have focused their attention on DirectX and done a lackluster job with their OpenGL implementations. If APIs like DirectX and Metal continue to proliferate, there will be less and less time and less incentive to maintain a good OpenGL implementation.