because when VII and VIII came out everyone played them and said thats final fantasy and they chose to ignore the old school knights, castles, kingsmiddle ages theme of the previous FF's because thye never played them. so when FFIX brought the series back to the old style all the millions of FFVII/VIII fanboys went around going nope thats not how a FF should be. because soo many peopel see themselves as experts after playing 1 or 2 games of the series.
thats why when FFX came out a lot of people were crazy about it despite the cliche story, easy gameplay and boreing characters.
also the character design comes into affect. cloud and squall 2 rugged looking guys looks like they were made to save the world. and their tough guy personalitys help with that. then comes little skinny 16 year old zidane kid with a tail. doesnt look like a hero in anyones eyes. but thats wrong. zidane always seems to come to the rescue. and his jokeing around personality makes him quite the interesting character fun character.
the story was very interesting. each character had there own interesting story that gets in some exploration unlike some other ff's. and an interesting theme of memories is included in it.
one of if not my favorite FF.