Since we are such a car-centric society, buses and bus systems are very different here. They largely serve the poorest communities who don’t own cars—and the average US town can be difficult to get around if you don’t have a car. For example, in my neighborhood there are no sidewalks. The road that goes from here to the nearest grocery store is very busy—constant traffic. Also no sidewalk. There is a drainage ditch on either side of the road. It is not safe to walk on the shoulder. This is just how things are unfortunately set up in newer areas where people are expected to drive everywhere.

That being said, Greyhound is the biggest, oldest, most well-known bus service. It is meant to travel distances. If you ride one, you soon find out how slow it is. A trip that might be an hour and a half drive becomes a three hour bus ride. You stop at every small town along the way. The “stops” are often at some random gas station in the “poor” part of town. Anywhere the bus can turn around.
If you ride Greyhound you see many small towns and always the dingiest, grimiest part.

The depots and official stations aren’t much nicer, most of the time.

However, the staff and drivers always seem to be good people! I’ve had nothing but helpful, friendly encounters.

Riding Greyhound with the rest of the non-driving (often down-on-their-luck) passengers can be a lonely, sort of sad experience, hence the songs and/or movie scenes. But if you have the right attitude, aren’t a snob, and know how to take care of yourself, it’s a decent, cheap way to travel.

FWIW, I’ve ridden buses in the UK and it’s a different experience.