Presumably for the same reason looking out the windshield helps with car sickness.

There are apps that show an overlay of moving dots on your phone which help with motion sickness.

	▲	onionisafruit 2 hours ago \| parent [-]
		That’s built into ios now too. It helps me not get car sick so quickly when I use my phone for a minute or two at a time, but I still can’t do what I want to do, which is read in the car.