Why is The Shawshank Redemption #1 on IMDB

For as long as I can remember, shawshank redemption has the highest rated movie on IMDB. Don't get me wrong.It's a great film, but is it really number one? Is it really the greatest film of all time? I always wondered why not Casablanca, or the Wizard of Oz, or Citizen Kane? There are plenty of other serious contenders for this title. Why this one?