Why do you think the characters in FF games,have such big weapons?

[Martyr]

The size of the monsters that they fight requires it.

Think about it, man. Even if you had the best sword ever, it would be wasted on a monster in comparison to which it is the size of a toothpick.
Unfortunately, that means that the FF Warriors have to learn how to use unusually large weapons as opposed to those that would be effective on humans/medium sized creatures alone.

That's flimsy. You could also say that the huge weapons are much too bulky for fighting enemies like lizards and such. It's like killing a fly with an A-Bomb. Plus, magic can be as effective (if not more so) on the big enemies as swords and such.

It's roaches that survive the A-Bomb, fool!
My position stands!