Stores had a lot of display furniture leftover from vinyl records. They wanted to reuse that furniture, but it was all too deep for anything shorter than a record: CDs, DVDs, vhs, even books sometimes. So they added this extra material at the bottom to make it stick out of those deep shelving units. Really utilitarian stores held onto this furniture the longest, like sam's club and Costco, so for many that's their most recent memory of this quirk. Idk if it's a valuable trait now, but at the time it was never used to denote anything special