The fines have to be heavy to make it work.
I rode the subway system in Munich a few years ago, which also has/had an honor system. I paid, but it’s my understanding that the fines are heavy if you get caught not paying.
Doesn’t work without enforcement. And such enforcement is a precursor to a police state. I never liked that fare system, even though I always pay the fare; it’s the excuse for the “inspectors” to be there that bothers me.