I'm not arguing the point that they should have more costumes, because they should, especially their first outfits… but as a design priority it makes sense to take something that's iconic and covers a lot of ground storywise. For the most part, that means Enies Lobby outfits, since that was the longest arc in the first half of the series by far.
I would much much MUCH prefer they put that time and effort into creating a new character than over designing costumes. (And Jinbe needs his orange back, I hate his green outfit)
As is they kind of got screwed by the timeskip happening while they were making the first game in the series, so they had to overwork the same characters twice, with major changes on several characters basically requiring a from-scratch approach. If not for that the roster would likely be much better.
@Omega:
Robin only wore that outfit during Water 7/Enies Lobby, no other arc.
Which was a huge chunk of the series she was involved in, with her most memorable story arc and most iconic scenes, which is what they would want to skew closer to for the cinema cut scenes. And the game includes her first timeskip outfit. For all intents and purposes she basically had
-Alabasta, Skypeia (which looks like a Nami outfit), Water 7, Timeskip, Punk Hazard, Dresserosa
They've got the two most iconic of the bunch. Sure her white coat/cowboy hat thing is fairly memorable, but it would also involve the most work in redesigning her clothes to apply physics of the flapping coat and extra elements and such.
Really, most of the strawhats are going to have like 8-12 fairly distinct outfits to choose from (not counting things they had for a very short time.) And in general, either their very first outfits or the Enies Lobby ones are the best bets.
(All of which gets thrown off by the likes of Chopper, Franky and Brook, who had very few outfit changes, mostly due to timing in the later cases)
Nami does have a lot of outfits. Usopp however pretty much has the same amount of outfits, if not less than Zoro.
A lot of her stuff is kind of t-shirty, so it SHOULD be easy to implement more, but…
And Usopp has had a lot more variety than you might think, its just generally been pretty subtle, an element here, a shirt there, an additional accessory... much like Luffy's changes, it doesn't really register much in black and white since the base style is consistent, but its very prominent when in color.
I actually prefer the plain white shirt to the one in the game. it looks cooler, if Oda didn't like it he would have changed it a long time ago. Plus Zoro has still has other outfits they could choose from.
Usopp's only seems the same, but there's always a new element on it, while Zoro keept the white shirt getup intact.
You only think that because you're remembering the first 100 chapters where it didn't change. But after that?
Zoro ditched the plain white shirt after Little Garden. He had something different in Drum, (coat) Alabasta, (desert attire) Skypeia (goggles and blue tank top), Davy Back (Buttoned white shirt with collar) Sabondy (striped shirt)… and in-game Zoro is wearing basically his Enies Lobby outfit.
Which again, one of the longest most iconic arcs.
And since the timeskip he's had his starting outfit, coat/shirtless on Punk Hazard, and black suit with fake beard for Dresserosa.
All that said, they've randomly included Luffy's carp outfit, so who the hell knows.
(I also wouldn't be shocked at a "Lucy" costume, since both Luffy and Sabo could use it. Heck, I forsee fake beards for all as DLC.)