I don't think this game exists just for the story, but I do feel that there's another factor that people aren't considering. Yes, it's a revolving door for a lot of people, but even so... is that entirely a bad thing? Obviously the ideal is to be able to retain subscribers and grow the population from expansion to expansion, sure. But with how competitive the space is and how much of a time investment MMOs are, that's a big ask. What if you also look at it from this perspective: If FFXIV did not offer the FF experience it does, how many of those people who buy in for the story would buy in at all? We're talking buying the game and expansions, maybe a 3 month or 6 month sub, and possible bringing a few friends with them for the ride. So after that maybe they leave until the next build up of content. Or maybe they never come back. But is that investment they made insignificant to contributing to FFXIV's success?
I don't have the receipts so I don't base my opinions around the bottom line.