Well in many versions of the story, Jor-el and Lara actually intend
for their son to go to Earth and become an inspiration to the people, and to use his powers for good.
So it's not much of a stretch to think they might have made his Kryptonian uniform look a little more colorful and dynamic for that reason. And it's not like capes originated with superheroes or anything. They can also be a sign of royalty, or something that people on Krypton just liked to wear.