One interesting aspect of limiting taxi numbers is that, as far as I understand the history, the first instance of doing so was imposed on taxi drivers by the public, rather than imposed by taxi drivers for guild-type reasons. London passed (one of?) the first taxi-regulation laws in the mid 17th century in response to popular outcry about the rapidly multiplying and unregulated hackney carriage operators; the law tried to bring order to the sector by both regulating the equipment & drivers, and putting a limit on the number that could enter the city.