So first you develop your game for Windows on DirectX, and than you make a port to OSX/iOS/Android using OpenGL, and than if you're lucky you make a port to XBox and PS4, maybe WiiU. Graphics pipeline rendering code is really small and simple part of any game, usually in big games you do have different render code for different GPU series or/and platforms, but it's much smaller in comparison with everything else.
What's big and bulky - shaders themselves, but there are solutions to translate them between different available languages.
> What's big and bulky - shaders themselves, but there are solutions to translate them between different available languages.
Those solutions aren't really ready yet: https://github.com/KhronosGroup/glslang/issues/200
I might be harsh to say it, but current vulkan/spir-v tooling is more like a toy than production ready. If one need to convert HLSL to GLSL then one probably will use something like https://github.com/James-Jones/HLSLCrossCompiler
and IIRC one place just used advanced macros magic to make HLSL and GLSL from the same source code :)
What would be the point for them to use the benefit of cross platform API, if they need to write their own? It won't be any cheaper than using the existing lock-in.