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.
Once I’m in the air my backpack goes from under the seat to under my knees. Then I can stick my feet under the seat for that extra few inches of stretch. It’s not a whole lot but it does help.