The purpose of the medallion is to create a guild. In practice, the coexistence of ride-sharing defeats that purpose, subjecting all drivers to the risk of unlivable wages, and penalizing guild members with dues.

> subjecting all drivers to the risk of unlivable wages

but how? the market would decide how much a taxi driver earns based on the simple law of supply and demand. Unlivable wage for one might be a very livable wage for another one.

The consumers would massively benefit from increased competition.

You answered your own question. The simple law of supply and demand can create unlivable wages for one. By controlling supply, you decide what types of people can make a livable wage.

Maybe you want locals with families to have the opportunity to drive. So you control the supply until they can afford local rents and still have time to spend with their kids.

Of course, cities often turned it into extortion, but they don't have to do that.

Even before Uber and Lyft existed, taxi medallions didn't accomplish their goal.

Taxi medallions drastically reduced the number of Taxi on city streets which was the primary reason they where introduced.

Overtime the system was intended to do various things like hold drivers accountable which it very much did, as well as various things it failed at.

Because of the cost? You're really making me guess at your reasoning.