The repetition in the FF terrain has nothing to do with the tools. The SE artists or those who were comissioned to create it (maybe it was 3td party) for sure are fully capable to create one without repeating elements.
I can only think of 3 reasons

- saving time
- saving budget
- Performance issues

I think the terrain is not made of a large mesh but rather of a series of smaller tiles.
Those tiles are not connected and the engine simply does not calculate/render the parts that are not visible.
There are various ways and tricks used in game development and every engine has different limitations and features.

I am sure that the guys working for SE are capable people, the team probably had long discussions about the repeating tiles and for some reason they choose to go this way.