We know why, before ItTSV, Editorial wanted Miles to be different from Peter even down to the silhouette, Donny wanted to make Miles the new Venom but the movie crushed those plan when more people saw him as Spider-Man. I'm glad Cody went back to the OG because marvel messed his suit up trying to make him even more different than he already is. The reason why Miles dons red and black is that Sara saw his power set and thought he would be on a lot of stealth missions or heroics so she made his suit blend in with the city scape.