I wish to say quickly, I have nothing against them. but when I look at them compared to, say, Africa or America, I don't really see why these isles/subcontinent were so considered good to colonize and keep pushing in, especially when Australia is literally trying to kill everyone
The section on Oceania in the /r/AskHistorians FAQ has some good answers that together might help answer your question:
Did the English have any competition for Australia? And if not, why? by /u/mikedash
Why did the UK send it's prisoners to Australia, an island on the opposite side of the world, rather than somewhere closer? and Is anyone able to provide evidence of the claim that the British (I'm being intentionally broad in looking for really any evidence) declared Terra Nullius concerning Australia as a fundamental part of their decision to colonise the country? by /u/hillsonghoods