For par condicio, if they don’t do it, why do we? Stand in line, that is. It is a cultural imperative for us, where there are two people, one is first and the other is second, that is the fair way. Lines are about fairness. I got here first, therefore, I am the first to pass. It is a simply the way things are. Fairness is about applying the same rule, in the same way to everyone without distinction, at least that is what it means to us. Fairness might be defined differently in another culture, because it is culture-based value. In some cultures fairness is about treating each person uniquely instead of treating everyone in the same way – expecting life to be fair is not realistic and what is right often depends on the circumstance.
Or maybe we just have better eyesight and therefore when we enter a space, we see the others and get in line.