Well, car owners can use the same argument: public transportation benefits only people without cars, why car owners should pay maintenance of train stations, buses, trolleys, repair shops for those etc?
I can't come up with any such counterarguments for public parking. It doesn't benefit non-drivers in any way, and the people it does benefit mostly don't need public assistance.
Edit: who pays majority of taxes for road use? It's car owners. You have cheap buses only because car owners paid majority of the bills for road network maintenance and development.
[1] https://en.wikipedia.org/wiki/Mass_transit_in_the_United_Sta... [2] https://taxfoundation.org/state-gasoline-tax-rates-2017/
Gas taxes don't cover all road expenses. I looked at Virginia's data (since that's where I live) and nearly as much road construction/maintenance money comes from normal sales taxes as comes from gas taxes. Another substantial chunk comes from the Federal government, and the Feds pay out substantially more than they receive from the Federal gas tax.