Pay per signup or revshare?

What about the other profitable revenue streams like pay per click, pay per impression, per lead, etc?

Why arent these smaller payout, by higher revenue generating business models as popular in the adult industry as they are in non-adult where the average affiliate can make in excess of $500k a year?

Your thoughts, why do you think the adult industry is stuck on revshare and per signup for its payouts?

Regards,

Lee