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.
If their “carry on” does not meet the size restrictions they absolutely will gate check it at cost. That’s their fault not listening or reading bag size restrictions orbwillfully ignoring them in hopes of forcing an oversize bag into the overhead.