There doesn’t have to happen much in our peripheral vision. Actually, there doesn’t have to happen anything. The point isn’t to see stuff happening in your peripheral vision, the point is to have a peripheral vision of a scene at all.
Not having it makes something look considerably more artificial. Just look outside the window and then put your hands to the left and right of your head like blinkers to block your peripheral vision. Which view looks more natural?
Having a peripheral vision (even if there is nothing happening there at all) emulates normal vision better, as a result you feel more that you are actually there.