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.
Oh, well in that case I'll just stand during the flight, and remain seated when we land so other people who care too much about what strangers are doing feel more comfortable.