Once more to the breach dear friends.. Once more..
Where to begin..
Firstly I think you need to break down the defintion of what TB is.
JRPG style - TB but with no tactical movement. (TB)
Final Fantasy style - Active Turn Based (except for X) (ATB)
Strategic TB - Has a movement component. (STB)
The three styles are as different as RT and STB so lumping them all together dosnt work. It's a gross oversimplification.
For those who are not familiar with the styles they are as follows.
TB - No movement. The sides line up and combat is conducted via a series of menus. The actual game mechanic can vary considerably. From Breath of Fires very traditional skills format. To Legaia Sagas combo attacks (each direction key making up a part of a combo beat um up style).
ATB - Same as TB but the game dosnt wait for turns. A clock ticks away in the background and everything moves in real time. Opening a menu can pause the game (or not , its in the option menu) for you to input your moves. If you do nothing , then you end up very dead.
STB - This is the one most people here would be familiar with. And it traces back to RPG's roots in wargaming.
Movement is carried out over some sort of grid or via a series of movement overlays. Each character moves in turn, then waits for everyone else on the field to complete it's turn. Then it starts over.
When it comes to sales, which are what is important to those who are making the game. What works for one wont work for another. So using FF (which has wracked up in the region of 60 million sales) to support an arguement for an STB game selling well, is a fallacy.
Likewise without the SquareEnix moniker , other JRPG's dont do anywhere near as well outside of Japan.
STB sales are mediocre at best. That TOEE owes most of its sales to the D&D logo really cant be disputed.
To my knowledge no one outside of Japan has tried to emulate the JRPG or FF game style. But those solve at a stroke most of the things that make TB games irksome.
No STB has ever come close to the success of Biowares RTWP (real time with pause) formula , or Diablo's real time formula. So unless you can make one on the cheap, or you have money to burn then making them is generally not a viable option unless you can get some big name property like D&D which will carry the game.