Where? I've seens a couple of ghost subreddits with spam, but then you see the same with ghost fb groups, weird twitter profiles, youtube, etc On even moderately sized subs I've seen any that wasn't removed quickly by the mods.
People can say mods are too expensive for fb and twitter, but there is the dishonesty, instead of paying mods they pass on that cost to us with our pii while pretending it's free.
uptimeporn, for a very specific example from today. I wont link it because the spam is NSFW and probably removed by now, but- I saw it, so moderation effort is obviously not effective.
That does nothing to speak of “auto moderator”, fragmented rules/guidelines and ilk and the sheer effort involved by volunteers.
Even then: the spam gets through. But I agree that PII is not solving this.