Final fansty isn't that kind of ip. Different ones are set in different universes/planets, with different casts. There's a billion different things you can explore. One game is basically medieval, another is basically cyberpunk. The things you explore are completely different and the only similarities are the name of the ip, the names of the gods, and maybe the names of some of the characters.

There aren't many games you can make that argument with because of the way technology has advanced so much.

Elder scrolls v skyrim was easily the most successful, but your suggestion is stopping at morrowind which is an entirely different game. Tomb raider today is a different game from when it came out. Some ways for the best some ways for the worse. But there are always new things to explore. Even if it's just mechanically.

Sure you can make that argument over something like the yearly sports games. But these games are not yearly releases.