Celes' original outfit was probably too complicated to animate on a 2D sprite.
Good point... also, pale leather would probably look a lot like skin on a tiny FFVI-style sprite. I daresay she'd have looked naked if they tried to depict her in that outfit.
And the last thing they'd want is for one of thier characters to look naked
Particularly in the US version, what with the censorship of various enemy sprites that went on there!
Not my words Carol, the words of Top Gear magazine.