While we won't know for sure, unless someone from AMD comments on this; in fairness there may not have been any other way.

Nvidia has a large number of GPU related patents.

The fact that AMD chose to design their system this way, in such a roundabout and brittle manner, which is contrary to how engineer's approach things, may have been a direct result of being unable to design such systems any other way because of broad patents tied to the interface/GPU.