It's pretty important to realise that this includes student visas (600K - and education is a major earner for Australia) and graduate visas (200K) and 700K New Zealanders (who have their own special temporary class).
There are also 250K working holiday visas (ie backpackers).
The single biggest justification for our high migration setting (among the highest in the OECD) is ostensibly for skills we need to keep the economy afloat. I've yet to see a skills shortage closed by migration. And of course, skilled migrants are one of the smaller cohorts in our net intake -- we actually bring in more dependents than we do skilled workers.
And of course skilled migrants have dependents - they generally have partners and kids. Why is this surprising?
We get to set the terms of migration, because it's our country. I don't think we should be allowing students to bring dependents across, for instance, because they're students. We're already saturated with them, and could stand to be a bit more exclusive.