It doesn't necessarily have to stem from a trope, I just think watering down visual designs to be relatable gives you exactly what you said; a bunch of different people in gis. In games where people are throwing fireballs and doing superhuman shit, I'd rather the visual designs be more congruent with the game design at large. I wouldn't want to play a UFC-esque fighting game using a cast full of demons and mages, for the inverse example. I think it's important to have some very clear, distinctive colour palette (something that especially makes a lot of KoF's designs forgettable) and some visual flair that gives that character personality. Doesn't matter to me what's written in their bio if I don't get that feel the entire time I'm fighting.
Why would I want to play any of these characters, just looking at their visual design? Look beyond the obvious similarities in colour. What does it tell me about them? Reeks of blandness, with minimal attempts to incorporate what makes a character unique in their aesthetics. If I'm 5 or 21, I can't for the life of me think of why any of this would excite me or even get me to the point where I would consider animations or playstyles.