Just for example, in USSR people were allowed to travel one stop for free.
Not for *free*, it simply meant that taxes paid by everybody covered it. Drivers still got paid, as did people, who took care of entire infrastructure.
That said, paying for extended period of use makes sense, as it regulates the way people use the system. Preventing overburdening of network.
Public transport system should be alternative and complement to private transportation (by either car or foot), not its replacement.