The seats are assigned. People have been standing in line for 15 minutes now. Why on earth would anyone want to stand there, when they could just sit and wait until the line clears?
I understand wanting to get off a plane ASAP, but boarding? You just end up sitting on the plane, waiting for everyone else to get on.
I saw in a flight that the airline mistakenly sold the same seat twice, two persons were fighting for the same seat, and when the stewardess came to review, she saw the error, the flight was oversold and the second man needed to leave the plane.
They don’t do that mistakenly. They just realized most of the time a few passengers don’t show up so overselling makes sense to keep the plane full.