Yes, you're absolutely right, there's no possible other reason why someone over 6' crammed into seat with almost no legroom would have a strong preference for an aisle seat.
No excuse for not standing up to let someone in, though.
I've done that as I had a suitcase with me . This was on a 2 seat row behind a 3 seat row.
Some of the public should have to undertake suitcase training, a few years ago I was stood behind an old guy just getting onto a steep esculator going down at New York Penn Station, he lost the grip on the suitcase and it flew down the the full length of the esculator thank goodness no one was ahead of him. It was about 05.00am in the morning. Some Amtrak Police Officers came running over to see what was going on
I would probably do something silly at 5am!
I wish my job paid me danger money for travelling after a certain time in the evening. Sometimes when I just want to get home after a long day at work there are yobs and drunked people on the train which makes me feel unsafe.