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.
Bin designs are just now getting to the point where there is something like a 1:1 relationship between passengers and overhead space. Only a small fraction of the flights operating (at least in the US) have these bins, though.
Some of the new Boeing aircraft, as it happens, so it’s a trade off…