Silly argument, Vulkan also isn't available on Xbox or Playstation, yet dedicated game console platforms clearly care a lot about gaming.
There's also only a handful of Vulkan games, supporting D3D11 and D3D12 on macOS would make a lot more sense. But in reality, porting to a different 3D API isn't what makes or breaks a game port.
So if Apple would provide a similar D3D shim on macOS, all D3D games would suddenly become "Metal games"?
If Apple would implement Vulkan support on macOS it would be a layer on top of Metal (same as their GL implementation or MoltenVk). Running through two translation layers (D3D => Vk => Metal) doesn't make a lot of sense.
That would either mean that Apple needs to maintain two separate types of display drivers or create a new abstract driver interface which sits between Metal+Vulkan and the underlying hardware. That's just adding busywork with only downsides, both technical and organisational. Vulkan just isn't that important outside of Linux and Android, especially when most games are built on top of a crossplatform engine anyway.
There's also only a handful of Vulkan games, supporting D3D11 and D3D12 on macOS would make a lot more sense. But in reality, porting to a different 3D API isn't what makes or breaks a game port.