What's up with hanging up in movies?

Ok, I'm sorry, but I get soooooo pissed when I'm watching a movie or a show, and somebody hangs up without saying "bye" or something. I mean really, if I'm in the middle of a conversation with my pal and he hangs up just like that, I'd get pissed, it's like totally rude. I don't understand why directors keep making such a glaring omission, I mean, is it because it makes the movie flow better? I don't know, but it sure as hell doesn't mimic real life.