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.
This is a valid reason.
My cousin gets serious panic attacks and had to fly alone. He was so nervous, I had to be on video call to help him at the customer service desk. We worked out for him and he was standing “near” line for about 45 minutes, which was more comforting for him than just waiting in a seat.