Do you have a reference for that? Is Australia trying to give undue influence to fringe parties? Are the conservatives trying to promote fringe candidates?

In a leadership election, it's in their interest to have a clear winner with a large majority. In a general election, it's in nobody's interest and indeed, counter to the national interest to have a huge majority.

In a general election, a leader that most people find acceptable is preferable to a leader that most people do not find acceptable.