Well, that and as least he would have the decency to finish off the series with a small screen time. That, and at the time he might think that people would eventually overcome his role as an old dead jedi relative to his other roles.
Remember, he did have other movies, some of which are quite good actually. Then again, for mainish characters with a face in Star Wars OT, most actors do not have any other good movies//characters. Mark is basically whoring out the star wars sign, and haven't done much decent since... and lets not even get into Fisher...