I'm not sure why would someone do this if flying takes way less time and is cheaper.
Let's say you're in San Francisco and want to be in Santa Monica the whole of the next day. Your options are:
1. Wake up at 3:30am, leave the house at 4, arrive SFO by 5, flight at 6:30, at LAX at 8, get to Santa Monica at 9. You are now completely shattered for the day.
2. Fly at a reasonable hour he night before, and rent a hotel in Santa Monica. You have now spent more money than Cabin.
3. Go to sleep on a bus at a reasonable hour in San Francisco; wake up at a reasonable hour in Santa Monica. You've used less of your waking-time to travel, and have spent less money than getting a hotel.
The alternative is broken travel, lines, TSA harassment, and arriving at your destination a hollow shell of your former self having had the live and soul sucked out of you by incompetence, harmful lighting design and oppressive neon tubes and the brown noise of an aircraft engine sapping your very will to exist.
If you are flying there is a need to book a hotel to deliver the same experience of being in LA/SF at 7am refreshed.
That is the "free money" in the model, people can exchange sleep in a hotel for a sleep on a bus with pretty much the same outcome.