Hearing reports today than many other players tested positive after arriving in Australia and they are playing because they were vaccinated. Djokovic also apparently had covid at the beginning of December so he is more protected than the vaccinated players by any scientific, medical or logical metric. He also tested negative upon arrival, unlike others that were allowed to stay.
By all accounts, he followed the "rules", which is why he went in the first place. Then they changed the rules and deported him.