One of the reasons 1Xbit is still on forums is because some users ignore warnings to stay away from this banned site. Users who advertise 1Xbit have been given a red trust which makes it difficult for them to enter other campaigns.
I think the other way around, it's because forums don't moderate scams. If the forum will moderate the scam, then we will no longer see 1xbit campaigns on this forum. Also, mods may not think about banning campaign participants as long as they post something sensible, but if these participants post perfunctory and break a lot of rules, they will be banned.
There are scenarios on how an admin can ban a campaign, there are lots of guidelines you can read in this thread: