Power consumption, optimization for non-DirectX drivers, AMD could meet the parts demand from Apple.
Apple ha(d) really specific requirements for their machines, so I don't doubt the decision was a result of whatever specification being met by AMD and not Nvidia at the time. Nvidia seems pretty happy in cornering the high-end market and can barely keep the 1000 series in stock at the moment.
Alternative options: NVidia is too expensive per unit or most Apple customers could care less about dedicated graphics. I think the latter is most likely - they don't sell their products on specs.
Power consumption, optimization for non-DirectX drivers, AMD could meet the parts demand from Apple.
Apple ha(d) really specific requirements for their machines, so I don't doubt the decision was a result of whatever specification being met by AMD and not Nvidia at the time. Nvidia seems pretty happy in cornering the high-end market and can barely keep the 1000 series in stock at the moment.