Well, I think the question is why.
In my previous reply, i was thinking more about that there isnt really that much creative leeway in a Gran Turismo game besides stuff like making new cars, new tracks, tuning options and improving the driving physics. If people lose interest in this type of game, i would say that it kinda "kills" itself, its not really the developer's fault.
While in a game like Final Fantasy, there is much more creative freedom and more things that can be done, so here its more up to the developer which direction they want to take. If they take one direction and see that people arent interested in it, they can change it up for the next game. Its harder to do that in a driving simulator.
Its an interesting question though. I think maybe one of the biggest reason for it is that people have found other interests instead, and there arent enough new gamers that are interested in the games to keep it on the same level of popularity. Same thing regarding fighting games too.
