So what would you do if you owned an airline? Lose millions from holding 4-5 seats on every flight as a contingency in case you have to move a couple workers every now and then?
That's not what is happening. Having 200 seats but selling 202 tickets is overbooking. This practice should not be allowed.
Needing to move workers last minute could be mitigated if airlines hired more people and were willing to pony up on-call pay.
People will understand bumping a few passengers so you can fly the next 200. The problem is airlines are purposely not transparent about the process, they don't offer reasonable compensation, and they pick the people who get bumped instead of letting people self select.