The big taxi company I drove for was at the top of the food chain in the Phoenix, Arizona area because the cars were clean, cabs usually showed up promptly, and if there was a problem you could deal with the company and they'd look into your complaint.

The company started switching out to the Prius a few years before I started driving for them in 2012. My first few leases were for old Crown Victorias, because I couldn't show up early enough to get in line for a prius (some drivers refused to drive the Crown Victorias, for various reasons).

The company had economy of scale in their fleet operations that was hard to beat: mechanics who knew the Prius like the back of their hand, boneyards (for parts), connections in the automotive industry.

They couldn't compete with people willing to wear out their personal cars giving 'rides' for peanuts. The company eventually sold off their fleet of priuses and their taxi yards, and refocused on the other businesses (app-dispatched medical transportation, etc). The Company tried to build their own dispatch phone app. But it didn't work especially well - I think they eventually decided to cut their losses.

VIP Taxi and Yellowcab are still doing okay, but I hardly ever see the green prius taxis anymore.