>I sure hate it when Microsoft does it, but at least they have market share. Who wants to support Metal just to target the Mac?
Plenty of big 3D/CAD/etc players? In lots of creative areas, the Mac dominates still (despite stories about people moving to Windows nobody's going anywhere, where nobody = quite few creatives overall).
Besides, with Metal they'll target iOS as well, and that's a huge platform, and where most of the profits are for mobile.