You've provided no reason why you feel this way other than "it's certainly not worthy to be one of the best movies of all time in my opinion". That's not an argument. You've also asked us to justify why it's a great film but without points to respond to you're just going to get a lot of generalities and stuff about cultural significance. That's not going to help you. Also, your only responses thus far have been to shoot a guy down for pointing out said cultural significance and to agree with someone else who shares your opinion. This suggests, as is often the case with these posts where some rando feels the need to share with everyone that a beloved classic didn't meet their standards, that what you really want here is to have your opinion validated.

Please don't waste our time. r/movies is privy to at least a few of these posts a week and they almost always bring nothing new to the table. You're not special for feeling let down by a film. But if you want a discussion on it at least bring more to the table than "I rated it 6 on my IMDb account".