For Windows I install a graphics driver by the GPU maker and get Vulkan support (according to wikipedia that is the case for Nvidia, AMD and Intel), since Windows allows drivers to offer such APIs without any specific support by Microsoft. With a Mac all the drivers come via Apple, without support for it.

Not just Mac. A big deal is ios' missing support.

Two major reasons:

1) Windows allows the GPU manufacturers to ship their own Vulkan support; AMD, Nvidia and Intel all do this, which covers 99.99999999999999% of all Windows machines where this is an issue. It's not as good as native support, but it's good enough.

2) Windows has over 90% market share on desktop. macOS has far, far less. It's a lot easier to get people to support your API when you have that kind of market share. iOS doesn't have enough market share for devs to ignore Android.

>which covers 99.99999999999999% of all Windows machines where this is an issue.

TIL Matrox only has <00.00000000000001% of the market. :(

Apple allows GPU manufacturers to ship their own Vulkan support as well.

It's likely not worth the vendor's effort but still.

If they were, say, actively revoking the certs of people trying to do this then it would be a different question, but it seems like the answer is the same for why anything gaming-related works worse or doesn't work at all on macOS: most gamers use Windows.