So MasterCard sets the interchange rate for each bank that it has an agreement with, but does not collect or receive that interchange rate. It seems to me that MasterCard is setting the price for each of the banks on behalf of the banks for something that MasterCard does not collect. You collect other fees, but you do not collect the interchange rate.
If I were to use an analogy, it's like Whirlpool Corporation telling Sears what its margin should be on a Whirlpool washing machine. Let's say Sears needs to have a $150 margin on a Whirlpool washing machine. Sears is not allowed to set that margin because it's been determined by Whirlpool. Sears pays another fee to Whirlpool, let's say $1,000, for the actual cost of the washing machine.
This seems to be somewhat anti-competitive in its behaviour and a contravention of the Competition Act.