Most developers I've talked to simply believe that a GPU specific photo mode is too much of a user splitting issue. What do they say to the people that own AMD GPUs, or any other future GPU maker? This is why many games have their own Photo Mode.
I own an nVidia GPU so Ansel would serve me, but I've come to see that Ansel is not embracing all gamers, it's only serving to sell more nVidia GPUs or promote them for free. Take that as you may.