Because the AFL has negotiated on behalf of AFL clubs and Telstra Dome.This is an example which I just made up.
Brisbane could sell 40,000 tickets at $20 with costs of $300,000
or Brisbane could sell 30,000 tickets at $35 with costs of $250,000.
They either make a profit of $500,000 or $800,000.
North Melbourne could selll 30,000 tickets at $20 with costs of $250,000
or North Melbourne could sell 15,000 tickets at $35 with costs of $200,000.
They either make a profit of $350,000 or $325,000.
Now explain why clubs who draw the same the crowd deserve to make the same profit.
Not the clubs and Telstra Dome.