Singles were pressed for radio stations, back in the day. May as well sell 'em if you're already pressing them. Sidenote: this is where the term 'B-side' came

Singles were pressed for radio stations, back in the day. May as well sell 'em if you're already pressing them. Sidenote: this is where the term 'B-side' came from. The A-side of the single had the song the music label wanted to promote, the B-side had some other song that most stations didn't play.