They could have put most of those TB3 ports and controllers in optional PCIe cards and the $4999 base model would still be Pro. Because the point of the Pro devices is to be the more-powerful option.

The iPad Pro doesn't have any TB ports and the Macbook Pro and iMac Pro only have 4 each so I think 12 is simply unnecessary for the "Pro" moniker in addition to greatly exceeding most people's requirements.