> I’d be surprised if the fees are meaningful on many transit systems, especially if you also throw out the costs of selling the tickets and enforcement.

Almost no public transit system has a farebox recovery rate even close to 100%. For municipal service (ie, excluding specialty transit), even 50% is almost unheard-of in the US, and only a few systems in Europe exceed 50% as well. In the US, the better transit systems have a farebox recovery ratio of 25% or less. In other words, over 75% is already funded by taxes, not by point-of-service.

Enforcement is a huge cost. In fact, in NY, the government has decided to spend increasing amounts of money over the last five years on police presence to combat "fare evasion", even though their own numbers show that the amount of money they are "losing" to fare evasion is less than the amount they have decided to spend on the additional police dedicated specifically to fare evasion.

So yes, it's a political, choice, not a fiscally rational one.