Well explained. It's quite hard to get a job with public transport nowadays but once you get into it it's quite hard to lose it. Anyway, trams have many more rules than cars and tram drivers see many more potential accidents than motorists who only drive for commuting. It would be quite rare that a tram driver violates enough road rules to lose his / her car license.
It's easy to lose your job with Yarra, just post something stupid on social media (that can be traced to you), critical of passengers or management.
I don't believe there is a legal requirement for a tram driver to have a car license, it's just a 'local' rule by the operator, and one that came about after the police tried to book a tram driver for speeding and found he didn't have a drivers license.
Shortly after that, it was made a requirement to have a car license first. However, drivers already on the road without car licenses were allowed to stay on the road.
They are probably all retired or otherwise decided to leave the job by now.
Really a car drivers license shouldn't be required - all rules for the safe operation of the tram should be part of the tram drivers training. Really they will be asking that prospective drivers have car driving license so they can be called into work at unsociable hours, not because they think it makes people better tram drivers.