Well, thus-far it has failed. We have Factorio, Tomb Raider and one of the Resident Evil games running on MacOS - most of which had to implement Metal by hand. If you're right, Apple's strategy needs to change.
Typically, if a game maker wants to make cross-platform a priority, they wouldn't target just Vulkan, they'd target a cross-platform framework. That would be true whether Vulkan was supported by Apple or not. And if they don't make cross-platform a priority, the chances of a mac port go down regardless.
So...
We're looking at the incremental gain of Apple providing first-party support for Vulkan vs the existing third-party support. Looks like a lot of work for Apple for little gain. Just doesn't seem worth it to me. Also, the Vulkan version would always be out-of-date since Apple would pin the supported version to an OS release, and would need to be conservative about it, since they aren't going to hold an OS release for Vulkan.
Really, Vulkan on macOS is much better done by the interested third parties, and the focus on Apple should be to get them to better support a Vulcan API on top of Metal.