Except that's not even how most bus systems work because most of them are majority funded by taxes with fares originally meant to serve as a stopgap but then slowly converted into a profit engine (usually after privitization). Fares are a way to gatekeep a service which your taxes already pay for, which I would argue, is by itself a form of theft.

As an example check out the latest MTA report only 26% of funding comes from fares, and that ones a bit in the higher end from what I've seen (NYC public transit, picked as the example a it's recently been in the news for issues with fare evasion)

All that aside, it's also worth noting that fare increases are extremely unpopular and it's not that easy to increase them without potential serious backlash (ie the mass protests in Chile a few years back that were in part set off by the fare hikes.)