The barrier to entry for a taxi service, in a sensible jurisdiction, is very low - put a sign on your car and start driving people around.

Uber and Lyft became so popular precisely because there are so many insensibly-regulated jurisdictions that made even this start-your-own-taxi-service illegal in order to create artificial scarcity. Highly-regulated medallion taxi services suck - both independent taxis as well as Uber are a threat to them because they're comprehensively better for customers. You literally have to legislate good service away for medallion taxis to work. And that's exactly what AB5 was.