The US government subsidizes farmers by a huge amount because for every dollar they spend they get a dollar and some change back in value. This happens all across different sectors and is beneficial for everyone involved. The farmers get a new pond for free and everyone else in the US gets a reliable, cheap supply of food. It's a win/win.

Public transport is the same way. It needs to be cheap so everyone can afford it, otherwise you leave huge swaths of the population without access to their basic needs, or you cut their already short supply of money even shorter. There's a reason progressive tax rates are ubiquitous across the world. By supporting public transport, you send people to places they produce value or spend money, increasing taxes earned across the board, while simultaneously reducing the cost of maintaining the roads because there's significantly less wear and tear. It's also CHEAPER to use public teansport. Cars are goddamn expensive! Repairs, insurance, the cost of it in the first place! A ride on the bus is like $2. You'd have to TRY to ride it enough to make it more expensive.

I digress. The point is that you indirectly get more out of it than you pay into it.

We're at a point (and have been for a few decades) that just taxing cars isn't going to fix the problem. We've demolished cities to replace them with vehicle infrastructure. If you tax cars without fixing the walkability, all you've done is make people pay more in taxes. You have to have the infrastructure before you can incentivize using it.