Maybe they have some algorithm that purges pages which haven’t shown up (or haven’t been clicked) in a long time? It would make sense to assume that something w

Maybe they have some algorithm that purges pages which haven’t shown up (or haven’t been clicked) in a long time? It would make sense to assume that something which hasn’t been clicked on for five years will likely not yield (m)any clicks in the future so it might be good to discard it. Concerning the auto generated sites e.g. for phone numbers or IPs it might be that people actually click on them quite often, hence Google keeps them in the index?