[DataGata]

The economics of public transit essentially ask for government involvement: operational costs are almost never paid for by fare prices, but instead are essentially subsidized. If the bus/train lines are doing well, you often get huge clusters of malls/retail/commercial buildings surrounding them, and they of course reap the benefits without paying any extra costs.

However, there are things like the Dollar Vans in New York that do actually fulfill the niche. They're also sometimes illegal.