It probably depends a lot on the industry. If your ticket purchase works, you never need to speak to a human being to ride a bus. Contrast this with cable companies - to sign up, you must have at least two customer service experiences: one to schedule the appointment, one to have the service installed. I think this accounts for their generally poor public opinion. They're not actually worse than most companies, but their customer service footprint is frontloaded and big.
I bet Greyhound receives an extremely low call volume in comparison. After all, by default, you don't talk to a human. Most callers with special complaints are probably routed to people with scripts that have most arrows point to "I'm sorry, but I can't help you. Do you have any other issues today?", and Greyhound has made the calculation that this will not impact their bottom line.