There must be a starting gun that goes off as the last scene of a feature film plays out. How else to explain the stampede for the door that begins immediately, often before the credits even begin?
It has always bothered me that people are in such a rush to leave. For one thing, what's the hurry? Staying a few more minutes isn't going to get anyone stuck in a traffic jam, and there can't be that many people with expiring parking meters.
There's also the rudeness factor: Those of us who like to savor the experience for a few minutes, or who maybe want to check the credits for the wacky brother-in-law character, find our vision blocked by the exiting hordes. Especially galling are the people who just get up and stand there. Either they think they're somehow transparent (like the husband who sang "Mr. Cellophane" in Chicago), and thus people can see right through them, or - more likely - they care not one whit about what others might want to see.
Next time you go to a movie, try sitting through the credits. There's often nice music playing. You might see a name you recognize (I once noticed "Brooks Robinson" among a film's closing credits, although I doubt the producers meant the former Orioles' third baseman). And sitting there quietly will allow you to think about what you just saw - an opportunity you may never have again. Plus, I guarantee there will be a smaller crowd to contend with when the credits are finished than when they began.