I've joined a few subscription sites because there was just one thing that I needed and once that was downloaded I had no need to remain a member.
This is my problem which I alluded to before. Mine is a download-based service. I add new materials all the time but people know they can rip through the site in a few days with a scorched earth download binge...then do the same 6 months later when their membership is a week from ending. What incentive then exists for them to renew?