[dgroshev]

This logic breaks apart in high positive externality areas, like public transport (or indeed postal systems).

Public transport brings a lot of value to other businesses and communities it operates in that can't be directly captured in fares. Which means that if a public transport system is profitable and the goal is maximising total economic (and social) value of the area as a whole, the system either under-invests, or is too expensive, or both.

The classic economic solution to this is subsidies: capture some of the generated value in taxes, re-invest back into the transport system. However, this makes the business part of the whole arrangement almost meaningless, because the amount of optimal subsidy can't be objectively determined. It's impossible to distinguish a bad business losing money from inefficiencies from a good business asking for subsidies to optimise its total impact.

There are some peculiar arrangements that some countries and systems were able to create, like direct land value capture through transport companies buying and selling property. But those cases are pretty exceptional and for practical purposes don't scale.