Australia used to play in the Oceania qualification group. And, unsuprisingly, they were always the best team.
But, a team from that area couldn't directly qualify for the WC because of the low coefficient the teams there have. So Australia used to always play an additional tie of play of matches against teams from either Africa, the Americas, or Asia. And they even had a period of 30 years where they would miss out on the WC becazse of this additional match.
So they petitioned to be folded into the Asian qualifiers. That makes the qualifiers more competitive and eliminates the constant extra play off match.