It's still not that old (~10 years or so iirc), it takes time for a third party to be major contentender. Earlier on you're more likely to see third party wins in more local than national level elections.
It's not an insta-win for third parties. But that's ok, because local elections matter, and that's where you'd typically see results first.
Maybe it's just to me, but liberal/national coalition and labor seem like the two major parties, green is barely at the table still.
If you exclude the coalition, national has 4 times the representation of green, and liberal 3 times that.
Just my opinion here, but it's still two major parties, with the thirds coming up in ranks and getting some momentum going. It'll be a good day imo when the greens overtake the nationals (and maybe one day the liberals), but I personally don't see it as representative of the people yet. Improving, but still functionally two parties.