The reason for that IMO is twofold.
1) Earlier this year Collingwood came out and complained they were getting a raw end of the deal from the umpires week in, week out.
2) With Collingwood coming out and saying the above, Collingwood supporters think it is true, so as soon as they lose they ring up every radio station from SEN to ABC and complain about the umpires.
Thats why it becomes a talking point.