Most cities restrict the number of taxi licenses (permits, medallions, whatever) — that drives up the market value of these licenses (and costs to the consumer). Unless the city is issuing new permits, new entrants to the business have to buy a license from existing license holders. That’s both a barrier to entry, and a retirement fund for the seller. It’s also an expense that gets passed on to the consumer.
These “sharing” services have disrupted that comfortable monopoly. Usually, that’s good for consumers, and new businesses. It’s easy to understand why existing taxi companies are opposed to these services.
As more underground taxi, car rental, and hotel rooms come into being, the more city officials are going to put the kabosh on it. They get high tax dollars off of those services (it’s not just about the vested interests of those the corporate monopoly of taxi services, etc.).