Leaving when game is lost!

Why do people do this, and by this i mean when a game is basically over (forced mate, huge material difference etc) why do people leave the game without resigning? its anoying, rude, inconsiderate and immature among other things.

so I put this to you people that do it, why?

also, moderators, is there anything that can be done about it. i know they get a fair policy warning or whatever, but should we as players notify someone as well? i really hate having to wait at a game for 10 minutes!

 Because some of them hope you to resign the game because they're not moving. This is natural to some chess players who hate to lose the game. They also had receiving a fair play policy when they do this and can be banned.

 Some? To me it seems a bit more than that...

I stick with what I say because not all Chess players are like that. I only posted that because of what I'm experiencing when playing chess,

Going from "some" to "not all" does not sound like sticking to me, but more like getting a lot closer 

But maybe it happens more at the lower levels (where I'm at) than at the higher levels?

Wow. To make someone get up from the board and not play any more, that is better than a win. That is what chess is all about. If your plan is better than theirs. If your knowledge is superior to theirs and they realise there is no force on earth that can help them. Allow them their frustration and maybe they will be motivated to persevere and move onward. Who knows maybe they will champions and remember quietly to themselves that long ago they acted badly but now are helpful.

More of the time this happens when playing against a beginner.