I'm pretty sure it boils down to one word, which astoundingly is never mentioned in this article. Monopoly. The American government has seen fit to grant Greyhound a monopoly over most inter-city bus routes, like it has done for so many other lucky companies in so many other sectors. The result of monopoly is almost universally a worse consumer experience. I don't see why it would be any different here.
In Thailand there is no monopoly over bus travel, if you want to take a bus there are state-run options, private options, you name it.
So this is how a random middle-income country on the other side of the world, with a name that one former US President couldn't even pronounce correctly, has beaten the pants off of America. It hasn't (yet) succumbed to monopoly (in this area).