Because it's a bizarre request. You're asking for a benefit - perhaps one of the most costly ones to CX - before you're entitled to it, and then wanting to "escalate" when you haven't been wronged in the first place. And FWIW, you're asking on the route where CX has the greatest # of frequencies. You can probably just show-up and get on a flight around your time (perhaps even the desired departure) anyway. I imagine all of these factored into the poor experience you had with the call center.

Besides you not being GO yet....

...because MPC must contact a reservations manager to get a seat released under the seat guarantee. They cannot do it themselves. And each time they call with a request like yours where the answer is a guaranteed "no", they get $hixt for it because the answer is 100% "no". It's not something they are supposed to be wasting another department's manager's time for. They are very strict with the seat guarantee; you've basically misread the situation and misplayed your hand.

Elaborating, this entitlement is suspected to be rather costly to CX. The entitlement itself is being changed in March (no more less-expensive fares permitted) - presumably because it is a pain for CX. None of us are pleased about the change, but that's the way it goes. Right now since GOs and DMs can force their way onto flights with relatively inexpensive V fares, it presumably is a cause of overbooking situations and overall bad load management.

What fare class are you traveling anyway? FWIW, V is the lowest Y sub fareclass permitted for seat upgrade (going up to Y in a few months), and only full-fare J is permitted - no C, D or I.

have to agree with these sentiments.