please add more unique outfits

[kyuven]

And here I am wondering why in a game where people can dress like they came out of Tron, I cannot have a plain T-shirt.

If you look into historical outfits, there were MUCH more elaborate designs instituted before the simple t-shirt. "plain" T-shirts only really became popular because they're cheap to produce, buy, replace, and decorate thanks to mass production.
Eorzea, however, doesn't have proper mass production. Thus each piece of clothing is either made in an incredibly simple fashion (smocks, robes, and the like) or an elaborate work of art.
Plus the regular t-shirt can be a little...immersion breaking.