it's a bit complicated. remember AMD have quite limited resource. so in the end they have to be selective to which game developer they will give their full support. in general it was probably like this:And it was AMD's fault?
AMD sponsored games: both AMD and nvidia will work closely with game developer.
Nvidia sponsored games: AMD most likely will not work that much with this developer since they have no official marketing effort. unless the said game is triple A stuff that will get a lot of coverage from media.
when the issues with Project Cars happen some people blame that game developer working more closely with nvidia purposely sabotaging the performance on AMD GPU. even saying stuff like forcing PhysX to run on CPU causing slower performance on system with AMD GPU when in fact the game did not have any GPU accelerated function being used and PhysX will always run on CPU even for system with nvidia GPU. in the end game developer did explain what happen with their working relation with AMD and AMD never once denying it nor did they accuse nvidia and Slightly Mad Studios sabotaging their performance.