A good manager will exclude spam post from weekly count. They might have some demenad who is paying you for posting on this forum. If someone isn't capable to fulfil weekly requirements then he shouldn't apply for campaign. I believe those managers asking for a minimum number of post, their minimum requirement 25/30 weekly. And I believe this is really not too much. I think paying per post would encourage spam more than fixed post, for example If paying per post and there is maximum post 100 then users will try to get maximum payment. All users are not same but most likely 90% users will try their best.

I there there is life out of forum for everyone. But if you like freedom then no one forcing you to join any campaign. Like I am working abroad and my company always forcing work fast and there is daily fixed working time. So I have to follow them in order to get payment. Same like for signature campaign. And I don't it would be wrong if company/manager ask for minimum post count since they are paying for that.