Now he realizes two graphics + CPU equals three, and a triangle has three sides ...
By all reports the Mach kernel they have struggles with more cores, I remember reading an article how it doesn't scale well. Linux solved this problem back in the 90's but Apple is still behind the game. Did they ever really fix that? Don't know.
Regardless Intel also struggles to add cores without significantly jacking the price. Xeon's are crazy expensive, it's cheaper to add parallelization through GPU's rather than CPU's which the industry has recognized. The idea these days is to find ways to put your code on the massively parallel and cheaper GPU. Even in supercomputing they are utilizing more GPU horsepower than CPU.
So Apple is just correctly following the industry trend. If software could take advantage it would be fun to put some more GPU out in a thunderbolt cage. That would be interesting because the bandwidth should be adequate for pure compute tasks.