Escalators are nice. They are especially great when you're carrying a suitcase or are just too dang lazy for the stairs. They're also funny because they can never really break, they just become stairs. Escalators are fairly ubiquitous, from train stations to airports to malls to hotels. Since they are so common, you might assume that people would have a general comprehension of how they function. But you'd be wrong. So very very wrong.
There is something about the top of an escalator that makes people want to stop. Maybe it's the transition from being moved to having to propel yourself again, or potentially the change in altitude causes some people to become disorientated, or the change in scenery becomes overwhelming. I don't know what it is, but people (especially those traveling in groups) tend to stop right at the top of the escalator and just form a clump of people. Do they not realize that other people also use escalators and are also being carried to the top and are also going to want to get off the moving staircase and that by standing right at the top of the escalator they are impeding progress and potentially endangering the lives of all other escalator users!??!?!? Okay, perhaps I'm being a touch dramatic, but serious injuries do happen on escalators including amputation of digits. In fact there is a whole foundation dedicated to educating people on how to ride escalators safely and I'm pretty sure moving clear upon exiting is an essential part of the experience.
A similar phenomenon occurs in doorways. For example, after a movie ends people will congregate immediately outside the door to the theater, obstructing the main exit. Although not as dangerous as blocking an escalator, I suppose there is still an opportunity to be trampled. Mainly I hate it because it's just plain inefficient and I really really hate inefficiency (see here and here and here, and many others). The movie is over, my bladder is full, and you are in my way having a conversation with your friend about how you can't believe you ate the whole box of Jujubes. Instead of blocking the door, why don't you start working off those candy calories and move out of the way. And while you're on your way out, consider taking the stairs. I don't want to get stuck behind you on the escalator. I know your type.