WHY?!

If there's ONE thing that i don't get; its THIS:

Okay, so i say 'hey' to someone, and they to say hey back,
BUT i come on-line and find that they have deleted their account, sure fine i don't really care it your account do what you wanna do;
but when every one you were talking to yesterday has decided deleted their account, it makes you wonder why.

So, does anyone now why they do that? what was the point in the first place to even bother with it?

Sorry for my angsty post, I'm usually a happy person, but things get to me every once in a while.