to me, as a user of public transit, they just seem somehow more pleasant, in a way I can't really make sense of. I strongly dislike riding in buses and try to avoid it, whether part of transit systems, Greyhound/Peter Pan, or even high-end charter buses.
maybe if you had electric (no exhaust, quiet) buses with frequent reliable service, dedicated lanes almost everywhere, nice bus stops without hostile architecture, I wouldn't feel such a strong preference, but I'm not sure.
I'm wondering whether it's not just that I subconsciously dislike getting jostled around and feeling slightly carsick.