The reason why it's one of the most overrated films ever is because it was one of a very few successful weepies aimed at straight men and it makes them feel like they have a sensitive side. If something is acclaimed by white, straight men it suddenly gets taken seriously, while the many women's films and melodramas which have been doing the same for nearly a century keep getting belittled by the same demographic.
Straight boys, have a good cry at the film but don't fool yourself that this is profound or truthful or in any way authentic about it's period, place or circumstances or that it is a good film. It's no better than the equally ridiculous Bette Middler melodrama Beaches, beloved by just as many women and gay men as Shawshank is beloved by straight men. It's just that women and gay men don't demand that a film should be considered a classic just because it makes them a little weepy.