The northernmost tip of Australia is 5 km from Papua New Guinea. Instead, boat people take off from Indonesia in leaky boats too unseaworthy to get to where they are going, much less be turn backed, to land on Christmas Island which is an offshore territory. A strong swimmer could get to the State of Queensland from Papua New Guinea on a good day. A decent paddle boat would do the job.
If the PNG authorities tolerated people smuggling, their relationship with Australia would be jeopardised. On the other hand, there is plenty of votes at the ballot box in Indonesia from sticking it to Australia. Little wonder that a substantial part of the Pacific solution to illegal maritime arrivals by boat people is bribing Indonesian authorities to crack down on people smuggling.