Except externalities are a thing.[1] Externalities are positive or negative impacts on society that do not accrue to those who cause them. Typically, rail transport leads to an increase in land prices and rents, but these additional profits are not recovered through fares, but fall into the hands of landowners. For this reason, railroads have historically been funded through land grants. For the same reason, most infrastructure is government-funded, such as airports, roads, or schools.

[1] https://en.wikipedia.org/wiki/Externality