License plate relocation theories?

Ever notice something and then you can't stop noticing it?

Watched a movie set in 1968, and there's a scene where a guy wipes crud off a plate to see the state, and I realized how low it was mounted (on the rear bumper).  Today, noticed a couple things in the parking lot.

1. Already knew, but nearly every car made since 2010 is some type of gray/brown egg.

2. On all the gray/brown eggs, the plates are mounted in the middle of the egg, not on the bumper.

I have no theories on this, there's probably no good reason for it, and it doesn't impact my life in any way. All those factors combined equal... post it on the internet.