Like some of these other jobs, it's important to note that this is an entrepreneurial choice. You take some risk by being a cabby, such as securing your car and outfitting it with all the necessary devices and comforts. On top of that you do have to worry about maintaining the car. If anything were to go wrong with it, then you will be out of a job. Most people don't want to take that risk, which is where all the rewards come from.
This is a job that is in flux due to ride sharing, so that is something to consider. It's always a little scary to enter an industry that is actively dying, but you never know what may happen with ride sharing. If you don't mind being stuck in a car, dealing with strangers in close quarters, then this may be your ticket to six figures.