I've already mentioned this at least once. Imagine a crime where 3 entities are involved, and only 1 always gets punished for it. That's what has been going on BTCT for a while (albeit even less effectively in 2016). What should be done is, punish everyone involved:
1) Ban the spammers themselves.
2) Ban the managers.
3) Ban the service.
If the service does not care about the spam, then it should not be allowed any kind of back-linking from BTCT period
Even if all they care for is only exposure, this still doesn't mean that they are deliberately encouraging spammers. I think that any service would prefer good posters to spammy ones. There may be just not enough good posters currently looking for participation or the payment is too low that only compulsive spammers get attracted by such a campaign. But in any case, it is a campaign manager who first agrees to manage a signature campaign for the service and then indiscriminately accepts participants into it...
Therefore, the campaign managers are the ones who should be dealt with and where it will be most effective