I can remember living in Oklahoma in the 1970's and seeing the 1/2 dozen eggs in the stores. I've seen them in stores in Chicago, and in stores up here in Wisconsin.
I visited my daughter in California, twenty years ago, and saw them in the stores out there. I've seen them lots of places, when I travelled.
I think we are seeing them more often because of the Boomers. We like smaller size egg and dairy products. I know my friends complain when their families shop for them and bring back gallon milk jugs.