I have never worked on PS2 software or hardware but I would imagine it's more complicated than just port their engine to something new.
Problem is likely between "Does SE want to have 2 modern MMORPG in the FF IP" and money+resources required for such a task.

I think this ship has sailed like a decade ago but I kinda like the game as it is, but then I grew up with the game so I'm having both a bias and rose-tinted glasses.