Because they are looking to change a a number of games this weekend .. believe that it affects 6 teamsWhere is this talk of changing the fixture coming from? Its not as simple as swapping 1 or 2 games and if you start changing more you run into the same problem you are trying to avoid.
e.g. If we play Melbourne in round 19 instead of 20, Adelaide would need to play Hawthorn in Round 19 instead of 20 as well. That results in the same issue
It's all over the internet via Google search