He doesnt have to be, but if he wants to visit Australia he does. His choice.
Fact he doesnt want to get vaccinated however speaks to his selfish sense of self entitlement and complete lack of care for others.
Those who choose not to get vaccinated are choosing to exclude themselves from certain privileges including 5ravel to some countries, attendance at some venues and events.
If the crowd has to be vaccinated, so should the players.
And you are wrong about quarantine, unvaccinated entry with supervised quarantine is an optuss for Aussie citizens and PRs of which Novak is neither.