I wouldn't call them rare as much as they were done by the artists who could afford it. Stones, Elton, Wings.......bands like that could afford to pay for the extra printing, artwork, gate-folds, etc....on their albums, so they did it.
I used to have some of the best of the best from the 70's and 80's, then I would walk into a Goodwill on Saturday because the little lady wanted the 50% off sales, and the record bins would have all the lesser known artists from back when. Seeing those types of albums really put it all into perspective.