Currently sims use "campers" to increase the traffic of a sim. People won't be inclined to go there if its low traffic.
So Linden may have found a way that "campers" are not counted for traffic.
If they no longer count them, then there is no point parking them all over your sim, and logging them off means Lindens may save money.
Still not sure why AFK sims still seem to represent the highest traffic. ( not all the AFK's are full time AFK, some people there when they are not doing anything else, for example when they go to bed , to try to make easy money ).