There is a cost in using public transport. Inconvenience. Using a bus will rarely be as convenient as driving your car. There is also a significant benefit to others whenever someone uses public transport...reduced road congestion and reduced GHG emissions. Conversely using a car imposes costs on others and relies on heavily subsidised road networks. Car users are usually not paying thew true cost including externalities/consequences of their car use.

Therefore it is perfectly reasonable where possible to provide free to use public transport (funded by taxes on other road users who benefit from the reduced road congestion) to maximise public transport utilisation.

The ideal mix will vary depending on the market but in large already congested cities the benefits to most people from free public transport can be significant. Currently we often have the worst possible mix with substantial tax subsidisation of public transport but minimal use of it because there is still an entry cost similar to taking your car.

There is a difficulty in neoliberal Libertarian ideologs in recognising that sometimes pure market forces do not deliver the best outcomes.