It's all about money ... either directly (we know AMD did this in the 3DNow age for instance, so it probably still happens now) or indirectly through in house devrel "support", free licenses etc. If it was an issue of principle then the first principle you stand by is to serve your customers ...As to why CDPR went with nVidia is pretty clear to me.
On the upside, if they use physx that heavily all through the game at least the CPU paths will have to be properly optimized this time around. Although the next gen consoles being x86 are making it hard to only optimize for the consoles any way (hard and impossible are of course different things).