For example let's look at Destiny 2. It was announced that it's gonna run at 30 frames per second on Xbox One X. And that is a game that you can, according to the technical specifications, be run on Xbox One X at 60 frames per second.
But then, obviously, they're in a situation where they can't have it run better on the Xbox than on the PS4 because they have a deal with Sony
https://www.youtube.com/watch?v=q7nH9-H4YE8&t=9m35s