Probably because when your making a very long, semi-linear RPG, art assets take a long time to create, so you have your choice:
1) Beautiful Art Assets, shorter game
2) OK to Good Art Assets, longer game
3) Very good Art Assets, longer game, but uses alot of copy & paste (ala Oblivion, Mass Effect)
Now, when it comes to FF bucking that trend, its because they actually have money to do such. A Tales game sells ~1m copies, so Namco knows what kind of budget the game can have. A Final Fantasy game sells ~7m copies, so Square knows that they can allow a higher development budget, and hire more artists, and developers to create a "bigger" experience than Tales.
Give Namco $50,000,000 to make a Tales game, and I guarentee it's the best looking of the series :)
Back from the dead, I'm afraid.
