You're forgetting I'm paying for posts on every section of Bitcointalk including off topic and all those other sections nobody else will pay for. This also doesn't take into consideration the amount of bonuses and contests that go into the group. In the end it's easily worth it because we aren't telling you where you have to post and giving a minimum post count per week, if people want to take a break for a week that's fine. A ton of this campaign is also getting a 25% bonus for their posts from the avatar. It's not hard to profit when people can make $5-$50 or more for 1 post every week from contests. We also don't demand personal text space you can put that however you want or get a bonus for using ours. Stake.com signature campaign #1!
Don't get me wrong, I am all for a free market, and you guys can pay whatever the market will support.
With the above being said, most campaigns do pay for posts in the off topic section, but even if they didn't, participants in the off topic sub would need to make 90% of their posts in this section for it to make sense to participate in your campaign if they qualified for a better paying campaign.
In general, your campaign is paying roughly 10% of what other campaigns are paying. This means a participant would need to make 500 posts in your campaign in order to make the same amount of money in a higher paying campaign that maxes out at 50 posts/week. Looking at the various other campaign spreadsheets, most people do not even make 50 posts in a week.
Even if one were to assume they received the highest bonus (only one person gets it per week, and you only give bonuses to 5 people/week), they would only be making approximately 20% of what most other campaigns pay.
The result of the above means that anyone who will qualify for any of most other campaigns will not participate in your campaigns, which leaves you with a bunch of spammers advertising for you. Take a look at
this post for example, in what appears to be the span of a couple of days, one person was able to make 184 reports against 4 users in your campaign that were marked "good" by the moderators.
You really need to either personally or hire someone to manage your campaign more closely, and either not pay for spammy posts, or remove participants who make a lot of spammy posts. You should also do more to screen against poor quality posters. This will probably result in you not having many participants at your current rates, but I don't think there is any real benefit to having as many posts with your ad as you currently have.