Not only chipmixer and bitvest but there are also few number of campaigns out there that are paying per post . some have a minimum limit while others dont have . if you are a campaign that has a pay per post structure and does not have any minimum limit then thats good because you wont feel pressure . you can post as little as one post but that wont be rewarding at all but thats okay if that can make you feel satisfied .
Campaign managed by Hhampuz are required to have a minimum of 15 posts for reaching payout, but in Chipmixer, if you post only 1, you will still get the rewards, that's what I meant. There's no other campaign like Chipmixer. Everyone requires to have a minimum number of posts.
They are doing that to encourage members to be active, the company is expecting a good return of what they are paying on a weekly basis, so their budget has to be maximize and that will help more exposure of their project in the forum.