Simply put: a strong business model, where consumers can't but be seduced by their offer. They solve multiple issues while getting the gob done (move you from A to B) and they make it easy for you to switch from your previous solution to theirs. At the same time, they also solve the issue of drivers who want to have an additional income.
If you are interested in finding up more about strong business models (vs. weak ones which command what I call "booty call clients"), check out serenademaio.com