Like I said payrate are only subjected to minimum payment, projects that's are capable of paying more are free to increase their payrate pay rank.
However, it's not that as easy as for each projects to pay high amount initially, you know everyone wants least cost with higher output. Projects will try to reduce their cost.
On the other hand, imagine BTC is at ATH. 0.01 BTC = $200 for 25 posts max, I don't think with current rate, much people will be interested to post 25+ in a week (It depends on user too, Royse posts 100+ each week although he is not required to do so).
That can be worked on too, for each $5000 price gain of bitcoin the minimum payrate can be revisited and adjusted in a manner it would be suitable for both the projects and campaign participants. I don't intend project paying as much as your example suggested, I used the current ~$10,000 bitcoin price to make this suggestion. The idea is the participants are been paid poorly and when that's the case what do you expect the output to be like?
Garbage in, garbage out. Take a closer look at well paying campaign, the quality of post been delivered by the participants are way above the others, in some instances, the posts counts (irrespective of them been paid for those extra post counts or not) are even more because this guys are been encourage by the payrate they recieve. We're humans here not robot don't forget that, we work with emotions.