https://community.amd.com/community/gaming/blog/2015/05/12/o...
If I were Apple the best I'd hope for is their mobile games porting over to OSX. However, with the added performance of desktop is Metal really needed? If it works on a tablet I'd say there's a fantastic chance it would work on desktop with mere OpenGL.
Apple has a large and loyal customer base, and it's typically people who are willing to spend money on apps and games for their devices. Apple doesn't have to try and satisfy a bunch of legacy CAD vendors who don't care about consumer 3D graphics at all. And when Apple announces Metal, they don't mean they have a spec, they have an implementation that is going to have a significant installed base in under a year. They have a lot of advantages Khronos doesn't.
(In any case, is it yet certain that Apple won't support Vulkan on OS X? It wouldn't have been ready for El Capitan's launch this Autumn regardless. Maybe Apple will try to deprecate it (in the non-technical sense) as a compatibility option but support it anyway?)
If Apple supports Vulkan but with worse drivers than Metal, I'm not sure that's any better. OSX has roughly four times the penetration of Linux in the latest Steam hardware and software survey. I'm not sure it's worth it for most developers to deliberately target the second-best choice on OS X in order to pick up the handful of Linux gamers who can't/won't dual-boot Windows.
(EDIT: see below.)
[1] http://store.steampowered.com/hwsurvey [2] https://community.amd.com/community/gaming/blog/2015/05/12/o...
That seems like a far fetched theory to me. AMD and NVIDIA haven't released drivers for XP for ages. Vulkan support in Source Engine is nowhere near done, if it has even started. In the meantime Chinese players will move on...
Developers increasingly treat iOS as a must-have platform but OS X hasn't hit that level. In particular, many games are ported but noticeably slower than the same game running on Windows. This seems like an easy way to avoid requiring a bunch of OpenGL-specific tuning which wouldn't be needed for either iOS/Metal or Windows/DirectX and will thus not be a priority for many studios.