Photorealism is not the King anymore
In my opinion the main reason behind lies in the minuscule progress that the hardware showed in last, say, three years. Since the first PC's we had a rapid progress in all the subsets of computational power. Three years of lag were decisive in video cards. In raw CPU power, in storage and bandwidth availability three last years changed everything by changing slightly. There is no rapid progress anymore.
Most popular console is now four years old. The most popular game engine is three to five years old. Computational power and GPU performance have stuck the ceiling. So the only way to outperform the others is to bring something new, something more emotionally and artistically pleasing than FPS with 60fps with 29 new guns.
Catastrophic outcome of raw power AAA-style development was demonstrated by Mass Effect Andromeda. Others were more persuasive - «What Remains of Edith Finch» for example blends the art and software engineering together.
Photorealism is not a silver bullet for success anymore. And we are moving towards 2018 to rejoice that!