The problem is most porn sites are not profitable buying/selling traffic to today.
Thus, it is always up to the site to sell the affil or some will have a bonus waiting for the affil if they hit the minimum. But it never swings the way you are saying. If anything it should swing the other way.
Fact is there are sponsors who pay $100 a signup once in a while. Same deal They have confidence and they want the affil.
So paying for the first $100 of traffic on certain conditions still makes sence as you get a new affil and you both see how you do on your first $100 then if you do ok the affil stays on win-win...
You'd get to see some new traffic sources. Money talks.
BTW, who is coming up with the next $100 a signup. ND?
Would be nice.
There are a million paysites looking for traffic. The ball is in their court. They are the flower and must attract the bee.