It's very disappointing that Apple hasn't adopted Vulkan. It's not like they are completely against standards either. I believe they even joined the FIDO Alliance recently.
With Apple adopting Vulkan, it may actually stand a chance against DirectX and the majority of game developers might start developing for Vulkan first. And Apple would benefit greatly from that, just like every other Vulkan supporter would.
Although not an ideal solution, MoltenVK [1] does a great job at bridging that gap