There was a surge in minor parties in the Senate about a decade ago. In the (very large) Senate ballot you were able to vote for a single party, and their official preferences registered with the Electoral Commission were automatically applied to the entire form. Minor parties with similar policies were obviously preferencing each other, and preferencing major parties very low. (The whole point of a minor party, sometimes a single issue party, is a significant deviation from the uncontested policy agreed upon by both major parties). So the process was changed and now the voter has to manually nominate at least 6 parties on the Senate ballot form. The effect of this is even the motivated voter with interest in the policies of a minor party cannot usually name 6 that they prefer over the 2 major parties, and so one (if not both) will end up getting a reasonably high vote preference when the previous scheme would have seen them near the bottom. This further secured the position of the two major parties.The previous system was being actively gamed. Because the Group Ticket Votes flowed between candidates in unnaturally high proportions, it was possible to snowball your way to election from a very small number of initial votes. How small? Wayne Dropulich of the Sports Party initially won election with 0.2% of the initial first preference votes.
This possibility meant that there was a large incentive to create a minor party and join a large preference-sharing network of parties which shared little in the way of ideology. No-one knew who was going to get the Senate seat when the music stopped, but it was a pretty good lottery to enter. You may remember Ricky Muir of the Motoring Enthusiasts Party, who won election based on above-the-line preference flows from these groups: Bank Reform Party, Australian Fishing and Lifestyle Party, HEMP Party, Shooters and Fishers, Australian Stable Population Party, Senator Online, Building Australia Party, Family First Party, Bullet Train For Australia, Rise Up Australia Party, No Carbon Tax Climate Sceptics, Citizens Electoral Council, Palmer United Party, Democratic Labour Party, Katter's Australian Party, Socialist Equality Party, Australian Sex Party, Australian Voice Party, Wikileaks Party, Drug Law Reform, Stop CSG, Animal Justice Party, and the Australian Independents Party. That's right, the vegans of the Animal Justice Party together with the Shooters and Fishers - I'm sure that's all about well-considered ideology?
The problem was that the previous system gave you two choices - you could rank all of the candidates - often well over a hundred - or you could accept another party voting for you. The new system instead allows you to rank the groups, of which there is a far more manageable number (and the groups are far more recognisable to candidates in most instances than the candidates anyway) - or you can still rank all 100+ candidates, if you like - or as few as 6.
The system after the abolition of group ticket voting more closely reflects voters democratic choices. The big parties get a lot of seats for the entirely unsurprising reason that a lot of people vote for them!