Beacuse its really good.

reasons:

- huge production values/ unreached cinematic experience on consoles at that time

- very good and engaging battle system

- sidequests/ "achivements" to do after finishing the game, that were satisfying, if you managed to beat them

- unpredictable and arguably fantastic and immersive plot

- highly recognizeable and loveable characters

FFVII came in the right time and with the right people:

- The leap to 3D: By that time 3D was the novelty in every platform, SCEA even tried to shut down 2D games (thank god they couldn't do it), but in the JRPG world they needed a powerhouse game that took the lead in the transition, Final Fantasy VII was that game...

- Sony Computer Entertainment: When Square released Final Fantasy VI and developed Super Mario RPG for Nintendo, the relationship between them was fragile, and when Ninty revealed that its 64-bit system was gonna use low-space cartridges that was the final blow, Square was out and Sony made sure that they wouldn't go to Sega or return to Ninty (although those bridges were burnt by Yamauchi until Iwata replaced him), they made a plan for making Square ridiculously famous in the whole world, that included co-publishing Final Fantasy VII in the west and making an aggressive marketing campaign for it... Final Fantasy VII was heavily advertised and suddendly everyone wanted to have "this awesome game with the fantastic visuals" (hey, they were fantastic back then)

Final Fantasy VII was the title that brought the series into the mainstream (because of the 2 points described above) and because of that it was the 1st one to many people, of course the plot (especially the aerith final scene that shocked a lot of people), the music, the characters, the FMVs, etc. helped...

The reason is a combination of the jump to 3d.. and Sony's impossibly huge advertising campaign. FF's popularity skyrocketed after that.

Regarding the "jump to 3D" talk, please remember that it was a jump to 3D for the FF series. There were other 3D games around at that time, and certainly other 3D RPGs, contrary to jonager's statement.

Agreed with Anarch all the way! +2

It has the biggest ad campaign for JRPG ever in the West.

For the same reason the Wii is so popular. The game is just damn accessible and bearing hidden depths.

In other words because it's some real good stuff, no matter how much Xenogears and FFVI fans whine about.

Didn't being one of the few titles of the series to be released also for PC help it just a little bit? IIRC it was the first FF for PC too and I remember PC gaming magazines really raving about it, even some peculiar aspects that most PC gamers often didn't like as opposed to console gamers, were criticized very mildly and without letting them prevent the game from getting very high scores.