Sometimes people do leave a great deal of time in advance and still are late because of train issues. And I am not talking about people planning to leave one hour before curtain.
Once on my way to the city, my train was canceled 45 minutes into the ride because of heavy rains, and the tracks on the way to Grand Central were flooded. Not to mention I already completed half of the trip there. Because of the flooding, there was only one track open apparently. Issues like that can make you much later than you anticipate, even if you do leave earlier than you think you need to.
You cannot deny that you may run into circumstances beyond your control that may unfortunately cause you to arrive late. This thread is more focused on those who think the world revolves around them, have no concept of time and think they can show up when they want and be seated immediately at their request.
"We like to snark around here. Sometimes we actually talk about theater...but we try not to let that get in our way." - dramamama611