You've made an assumption, convinced yourself that it's right, and seem to keep arguing the point. Not sure what you're trying to prove.
Are you aware of how they handled this in the past when this would come up frequently?
This is probably the first time it's come up in 3 or 4 years. I don't know if it's oversold or understaffed. Doesn't matter to me either way. Historically this has occurred when the cruise was oversold.
FYI, when this used to happen on a regular basis, I think some people either lost their jobs or were reassigned, so yes, at one point their procedure on this was fairly incompetent, and they gave away literally thousands in upgrades, move-overs and refunds.