The official message of the Turnbull government is that the “Pacific solution” is intended to discourage the dangerous passage by sea and undermine criminal networks making money out of it. In that context, it makes sense to provide an alternative. The message is “don't waste money on a risky passage, go through the legal route instead”. On the flip side, it's easier to vet refugees and manage their arrival that way.
Without alternative route to refugee status, Australia's position would also be hypocritical and ultimately untenable. Beside loudly claiming that no one will ever be accepted in in the country, a major component of the policy is to get poor countries like Papua New Guinea and Nauru to take the people caught crossing irregularly on ships. Basically using Australia's clout and money to get rid of “boat people”, with the added benefit that it makes Australia less attractive than other potential destinations. That's also why Australia spends money on professionally designed ads: It's a communication approach more than anything else.
But it doesn't really solve anything, only displaces and freezes the problem. The conditions in the camps deteriorated quickly, with no long-term solution in sight, and Australia is still accountable for that. The current government only managed to stick to this policy because the US accepted to process a few thousands of these people. I am not sure whether increased participation in relocation efforts was formally a condition to that agreement but Australia would certainly be under a lot of pressure to participate in international efforts to relieve the countries most impacted by the current refugee crisis (countries like Jordan and Turkey, which take millions, not tens of thousands, of refugees).
One clear benefit of such an arrangement is that even if the country ultimately takes as many or even more refugees, it still makes the crossing much less attractive for the people trying it as they won't be the ones ultimately allowed to settle in Australia. I believe there were discussion about a similar agreement between the EU and Turkey at some point, whereby Turkey would take back a number of people stuck in Greece and the EU would in exchange take the same number of refugees from Turkey, selected and vetted through official resettlement programmes. The net flow remains the same, all countries contribute but the incentive to attempt to cross the border irregularly is reduced.