Understanding the aisle seat train passenger

Hi All,

A question I wanted to throw open to all of you which has always made me curious; why do some train passengers opt for the aisle seat instead of shifting over to the middle when someone wants to sit on a 3 seater?

I'm always judgemental in thinking that this person assumes they're getting off before their co-passenger who wants a seat; can someone please explain to me why I might be wrong? Are you 1 of these passengers? Do you prefer the aisle because sitting in the middle makes you sick?