It's a long, sad story. I'm sure the experts will provide all the details, but the short answer is Adobe has an old technology that they have given up on and are not really using but it drives the "approved " list of cards, and no one uses them. The approved cards are expensive and useless.
My understanding is a new generation of video cards is due this month that are supposed to be amazingly fast and not too expensive.
I am speaking as a business owner that is extremely aware of the true cost of doing business and NOT as an employee or representative of Adobe.
NVIDIA completely changed direction in their CUDA GPU development which threw a wrench into further development of CUDA accelerated Ray-traced rendering by the Adobe Team. Better options for getting objects into AE were being developed and Ray-traced rendering using CUDA acceleration was not living up to expectations anyway. Rather than limit further 3D development to one manufacturer of GPU cards and drivers and completely retool the existing Ray-traced rendering engine to NVIDIA's completely new system Adobe wisely decided that the greatest service they could do for their customer base was to devote the resources necessary to try and update a rendering engine for a small percentage of their user base based on a technology that was basically abandoned by the GPU manufacturer to a more efficient system.
We now have C4d integration and it's more powerful by far and has many more features than Ray-traced rendering ever would. Personally I never used Ray-traced rendering for a single project I was getting paid for. Even though I have computers with fully supported CUDA GPU's, it was still too slow to work with and too glitchy to ever use on a project I expected to make a living on. I did a few fun tests to fulfill my curiosity, but that was about it.
Have you ever had any luck with this issue since it was posted?