I believe it was a contract dispute between him and Topps... back then, liecnsing was ever changing. Topps had an agreement with the Players Association but not with the NFL for logos... so they could produce cards of the players, but couldn't use logos on the cards (or in the pictures of the players). Fleer had the opposite agreement, so they could use team names and logos but couldn't identify single players on their cards. This changed in 1982 when Topps started paying the NFL for the use of logos... I think Fleer continued with NFL Action cards until 87. But during that whole time, the Players Association allowed players to opt out of the agreement and handle their licensing on their own... Earl Campbell was the most well known example, but Joe Namath did for a shorter time and was missing from a few Topps sets also.
Comments
Contract disputes between him and Topps over using his likeness on further cards.
George Brett, Roger Clemens and Tommy Brady.