The real question should be: Why does a taxi plaque cost $50K? That seems like monopolistic rent seeking by the government, they certainly don't add 50K of value.
Taxi plaques are not unlimited - there are only so many. I have seen them release 20 more but how long do you think someone was waiting for the chance to get one? Supply and demand - same with marine park permits and 3k per permit might have been ten or more years ago - triple that today and then some.
A lot of the drivers do not own the plaque, they rent it from someone. The former president here, Pedro, I'm told has ten or so plaques - he ain't driving a taxi jajajajaja
I looked at getting a few taxis, was told by many people one million pesos for the plaque - I know someone that has two. The new moto taxis, now that the gunshots and fires have stopped is another one - I spent two weeks chasing info about that, very complicated with a very high risk reward..... No thanks
Look at the shuttles now at the airport, why three shuttle companies?? Crazy really - they all three have the same prices. Ferry boats, pricing nearly identical, today the new companies boat arrived. Maybe it gives the false illusion about competitive pricing....
What you describe in Warsaw is an ideal solution - allows the look of compitition and makes it easier to get a "taxi" - they go weeks without answering the phone at the taxi base or even their Facebook messanger.