There is no ripoff and the rules are clear. You can always cancel a bid until it is accepted. But once the upgrade is successfully accepted, then you lose it if you desire to change the flight.
The rule is clearly stated on CX website:
"Unfortunately upgrades cannot be transferred. If you choose to change your flight, your upgrade offer will be forfeited, and no refund or credit will be given. "
https://www.cathaypacific.com/cx/en_...y-upgrade.html