The Melbourne weekend public transport timetable is appalling. Trains run every 20 minutes at best, trams run every 12 minutes and buses even longer. There is a chicken and egg problem of demand vs supply. People won't take public transport because there are not enough services, and public transport companies won't increase services because of this.
There needs to be a circuit breaker to tip the balance.
Making the whole public transport a single zone on the weekend will seek to push the demand side of things. Getting more people on the public transport so the operators will take notice.