I have to admit in my 10+ years flying with CX I've never seen agents calling out for volunteers with cash as many times as I've seem US-based airlines do that. My personal experiences is more negative, at check-in the agents just lied to you that your flight may be delayed or cancelled so it's better to put you into an earlier flight or later flight (of course no flight delays occurred.)

I think it's because the routes I travel are popular routes with many CX slots so there's less incentive to do that.