Overseas teams usually lose in Australia for two reasons.
Their batsmen aren't used to playing on really flat wickets and therefore don't have a mindset to bat for long periods of time to build 400+ totals against accurate bowling and their bowlers can't take 20 wickets when the wicket is barely doing anything due to their pace usually being below ours.
When the tracks are juiced up, their bowlers are more effective and with our batting line-up they have a good chance to roll us for a below par score. Even if their batsmen are worse, if they make 150 and we make 200 obviously they have a better chance of winning.
The best example of this was South Africa vs Sri Lanka last year where this basically happened. Sri Lanka's mediocre bowling attack got enough out of the surface where they could expose a weak SA batting line-up.
Yeah, greentops tend to be equalisers because the outcome of the match depends on the rub of the green RE the toss, and also on how well you catch, because both sides will generate plenty of chances.