Users in the forum, and participants in campaigns have to do their works well in order to help to build up good reputation for the forum, for companies that hire them with their signatures.
If the forum damaged by tons of shitposts due to signature, theymos will destroy all signatures.
If companies don't get benefits from their participants because shitposts don't catch attention of readers, and don't have effects for companies (adverse effects, in some cases); companies will stop running their campaigns after short time.
Some of those signature campaign managers do end up having to filter through a lot of bullshit, but it is likely NOT good to get too personally offended by it. You are correct that the incentives to join are not going to be too much, but if the signature campaign is paying in bitcoin, and the participant is just continuing to hold his payout, the amount of dollar value can really add up in the future, which will definitely inspire some folks to participate, especially from low income locations.
I still don't know why you decided like that, because you are obviously a strong poster, so you can keep posting, to clean up the forum, to help other forum users, and still receiving some bitcoins from reputable campaigns. Why not? If you want to give open slot for others, appreciated your kindness.
Pretty much I stopped participating in signature campaigns in early 2018 because I just did not want the ongoing hassle. I had acquired more than 3 bitcoins in about 2 years from the ones that I was in.. but still, when the BTC price went shooting up, I just began to think that my BTC holdings were way more valuable than trying to chase after more.. so that is kind of a personal choice based on circumstances.