So they go faster.
They're either going to be red, blue, or green I guess. Based on how our eyes work. Our sun is greenish yellow, right? It may be no more complex than color theory and an indication that there was more heavy red stuff in the protoplanetary disc than blue or green. A lot of words to say it's red because it's red. Not very satisfying. Maybe there's a better reason.
Most of the not-star solar system is red though. Just Jupiter being mostly red makes that true. So really it might just be initial conditions. Might just be that simple. Probably also something fundamental about how light works. Earth is pretty red underneath the water and biomass.