alt Hacker NewsBecause DirectX is a success and Metal is not.
If Apple wanted Metal to be a success then they'd need Windows devices to support it, and ideally a console too (like DirectX with Xbox).
There's a lot of bad things you can say about Vulkan's market position relative to DirectX, but it's clearly more successful than Metal. More games and work applications are written in it. I don't see what Apple gains from going their own way. Maybe Vulkan will rot by committee like OpenGL once did, but that hasn't happened yet.
Even without a standard, people will create abstractions on top so all you need to do is add support to those abstractions. If needing to conform to a standard was hampering Apple's ability to get developers to make software for their platforms they would add support. It's obviously not materially affecting them.