not surprising. advertisers are crazy about ppa options as they have the full benefit. secure income, free branding and not a cent to lose on ppc. marketing risk distribution completely to the disadvantage of the publisher.
the problem will be to find enough - and i say dumb - publishers to join the program and sacrifice their valuable ad space. see, you have to actively promote the products for the advertisers, you are a kind of outsourced sales department. compared to ppc, it will pay off for the fewest.