That and the fact that Apple just doesn't seem to care much about 3D support... the 3D stack is about 3 years out of date now, GPU drivers as well (and nVidia etc. can't update them). Yosemite had NO updates to the GPU drivers or OpenGL support at all and currently it's still about 20-30% slower on the same hardware compared to Windows.
If I'm a bit cynical, Apple is deliberately refusing updates just so they'll be able to tout huge 20% performance improvement of their proprietary Metal when they bring it to OS X.
If I'm a bit cynical, Apple is deliberately refusing updates just so they'll be able to tout huge 20% performance improvement of their proprietary Metal when they bring it to OS X.