Public restrooms in Czechia often can take cards now. I imagine it works similarly in Sweden.

As an American, this concept still makes no sense to me. It's public infrastructure of a sort, don't real estate taxes in the surrounding area pay for upkeep and repairs?

See also, subway stations in Japan, which IIRC operate under a similar model.

Transit is so good it replaces cars. That means users can afford to pay for it.

Free transit is a terrible idea because e.g. it means tourists don't contribute and anyone who passes a tax cut will have defunded it without the actual users being able to help.

How does this account for people who live paycheck to paycheck and don't have cars?

This is literally how they get around - asking those who can pay the fare to subsidize them doesn't seem like that much to ask.