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.
This is a fascinating piece of historical context. Regulation has a demand side, nut just a supply side.
Worth keeping in mind.
Likewise, the public tends to demand regulation when the cognitive overhead is prohibitive for an individual,[1] bur more economic at scale by a neutral party. The latter is especially efficient ex ante as opposed to ad hoc.
Again, there are multiple views on what is rational, light and efficient depending only on abstraction and completeness.
[1] Eg, when faced with too much choice, under too small a timeframe, with opaque or imperfect information, and costly information processing techniques.
