I don't think it's so much the exclusivity but that if you are a loyal CX customer saving to Asia Miles at its relatively low earn rates, it takes more points to redeem seats on CX with more restrictive rules than those who earned AA and AS miles much more easily. So it feels like the airline biting the hand that feeds them.
There is also the fact that there is limited availability, especially after the devaluation, and particularly in F. So every seat that goes to a partner redemption is one less available to a MPC member.