An observation made, admittedly, when I regularly used a commuter train rather than one where most of the seats are reserved, but it came back to me today and is no doubt still true.
Many people will sit in a window seat and deposit their bags, coats etc on the aisle seat next to them.
I prefer an aisle seat, and make a point of not depositing my worldly goods on the seat next to me.
Once each pair of seats has been filled in this way, the next person to get on the train has to find a vacant seat. Nine times out of ten, they will ask me to move so that they can get into the empty seat next to me, rather than ask someone else to move their bags.
Is this because most people have such a desperate desire for a window seat? Or is it, as I suspect, because it's somehow easier to ask someone to get up so that you can sit on an obviously empty seat, than risk appearing critical by asking someone to move their bags?