In instances, it's people moving a small amount to reset it. It doesn't take much. That said I mostly see it abused in MSQ roulette since it's difficult to initiate a kick with so many back to back cutscenes leading into fights. 24 mans people usually get kicked if they truly AFK (not for like 2 minutes between fights; long enough for everyone to see they're not there), though yes, it is a bummer when the loot timer gets in the way.