The difference is the Windows driver model allows IHVs to implement Vulkan alongside the proprietary DX12. Microsoft may not support it but they've provided the

The difference is the Windows driver model allows IHVs to implement Vulkan alongside the proprietary DX12. Microsoft may not support it but they've provided the framework to let it happen anyway. In contrast Apple exclusively controls the macOS graphics stack top to bottom, so as long as they don't explicitly support Vulkan they're forcing developers to use their proprietary API.