Aside of the technical merits there are also the questions of open vs proprietary, platform availability etc.
Also the question of "technically best solution" is also fraught with subjective definitions of "better". You also want competition in approaches. E.g. Vulkan might not have happened (an we would be stuck wit OpenGL) without the newer more modern GPU APIs from Metal and DX12.
Wouldn't it make sense to simply implement the technically best solution everywhere?