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.
Overhead space. The only upgrade I pay for is boarding group, and I want to maximize my upgrade purchase, so I want to be at the front of group 2.
I only travel with an appropriately sized carry-on but I’m a bit tall so I can NOT have the bag by my feet.
So I want to guarantee I have the overhead right above my seat.
I also generally work on the plane so I can get my laptop and such out easily while standing at my seat, then put my bag up worry free.
Also, when you will likely be sitting for 2+ hours, I like to stretch my legs a bit before then. I don’t need to sit at my gate for an hour before going into a plane to sit for 3 more hours.