Running into large packs on official...

How do people keep running into these, i only play on official. I stay to the outer home caves to level, i hide when i see a group or move away if the map shows red and have never had an issue with Mega packs at all. I've killed plenty and died plenty. i've also had mega packs kill me now and then but only when i went right to them, usually when i was watching fights or something and wasn't paying attention to who was where. How do people get killed over and over by and easily avoidable Megapack? I see it on here every day? How does a mega pack get the jump on you?