If someone forced to meet high number of posts every week then chances of a good poster slipping from their quality posting behaviour to meet such requirements but having 25 or 30 will not be a problem for a poster to reach every week but number of post doesn't alone set the quality of a campaign if they have no restrictions to join in their campaigns.
Cryptotalk participants aren't forced to meet any requirements, there is just a maximum payout of 10 posts per day(And it isn't compulsory to make), which they would pay for, and I do not think that is too much, I can comfortably make ten posts a day without the slightest hint of being called a spammer.
Some campaigns require 25-30 posts per week to get paid, but cryptotalk participant could make 10 post a week and still get paid, what this shows is, it's not the campaign that's solely to blame, users can decide to be spammers whether they are on cryptotalk or not, it just happens so many(spammers)are on that very campaign as the number(participants)is so high.
Yes, there are no restrictions to join the campaign, but yahoo with the effort of the community are breathing down the necks of the spammers, you can join in on the act by reporting a spam post when you see one.