You are missing a point!
They won't give up because they don't really have to rank up to higher levels to earn money from the forum with current rules.
Why is that?
If you have experienced enough in the forum, you would realize that signature payments for Member rank usually double of for Junior member rank. Yeah, that's the point, shit-posters don't have to try to rank up, they have another option, which seems to be better, more comfortable for them.
2 Junior member accounts instead of 1 Member account. That's enough. Keep posting shits and get money, instead of putting lots of real efforts to rank up and get the same amount of payments.
That's right, sooner or later those shit posters will eventually give up on making their way up to the rankings and will be forced to join social media campaigns as they will realized that they will not be happy on what they will earn on signature campaigns with their current ranks.
Merit system will keep shit-posters stucked at their current ranks. In the future, when more and more campaigns require minimum number of merits to join, shit-posters will be eliminated somehow. When they can not join any campaign in the forum, they might leave and find others better places.
The time since the new system has been implemented is not yet enough to eradicate all those members but we can see that it made a change significantly.