Heres Unitys World Level Design Director, Nicolas Guerin:
At Ubisoft for a long time we wanted to push 60 fps. I dont think it was a good idea because you dont gain that much from 60 fps and it doesnt look like the real thing. Its a bit like The Hobbit movie, it looked really weird.
And in other games its the same like the Rachet and Clank series [where it was dropped]. So I think collectively in the video game industry were dropping that standard because its hard to achieve, its twice as hard as 30fps, and its not really that great in terms of rendering quality of the picture and the image.
The games creative director, Alex Amancio also chimed in that 30 fps feels more cinematic and that it actually feels better for people when its at 30 fps.