He didn't quit chess. He just quit competitive and public chess except for a later Spassky match.. He continued to play. He proposed his time control scheme in 1988, then chess960 in 1996. So after Fischer "quit" he contributed more to chess than many here including myself are likely to ever do.
Fisher random aka chess960 may end up being the most significant contribution to chess since Indians introduced chaturanga to the Persians.
Many consider Capablanca to be the greatest natural chess player of all time. Karpov puts Capablanca in the top five of all time.