Most of them are from Chipmixer and Bestchange's campaigns, and some of them are from the rest of the campaigns? These campaigns force members to create 50 or 25 topics per week, so the frequent posting will make them get merits regardless of the topic.
I disagree with the idea that frequent posting will get you merits; instead, it all depends on the quality of your postings, not the amount; I've seen users with 10 merits in their first three posts, as well as those with over 2000 posts with zero (0) merits. It would have been different if campaign members were required to earn at least 5 merits per week in order to remain in the campaign, rather than a weekly post count.