Human bugs: why do players join a battle and then not play?

This has to be the single most annoying aspect of WoW, user sabotage. Wtf? I get that sometimes the internet drops, etc., but this happens a lot. Just happened again, the cruiser next to me never played. Can there be a system put in place that if you do that, oh, say 3 times in a week, your account gets deleted. Thoughts?