Karin actually got considerably redesigned.
While I personally would have loved to see Ryu and Chun completely redesigned, I can understand why they didn't change them. Refusing to change classic costumes comes with a price. Changing up classic outfits also comes with a price.
It's basically Capcom-style vs NRS-style.
NRS gives zero f*cks. They will take their poster boy and kill him off on a whim. They will turn him into a zombie. They'll turn him into a bad guy. They'll change his clothes non stop. The benefit of this is that it's kind of exciting and unpredictable. The cost is that your characters have less weight. They are "cheapened", in some regards. They don't feel as human.
Capcom maybe gives too many f*cks. The legacies of Ryu, Chun, and their entire cast are VERY precious to them. Iconic status is not something easy to achieve. And, yes, the cost is a sense of boredom and predictability. Ryu is Ryu. You can predict what he's going to do in almost any circumstance. However, the benefit is strong, consistent character design. Characters with weight who, like real people, are very difficult to change.
To be honest, I feel like SF5 is the closest to NRS-style that SF has ever been. Yes, Ryu, Chun, and Gief are unchanged...but I think they're like a buffer to ease us into the Birdies, the Nashes, The Vegas, the Bisons, The Dhalsims. Everyone else has been spruced up more than any other SF game. I feel like the design team is being a lot more adventurous and "not-lazy" than we're giving them credit for. I wouldn't be surprised if Ken's redesign started fights within the design team, lol.
