When I did an Etsy app, there was no affiliate program, which seemed to largely stem from the fact that Etsy charged to little to sellers that they were barely making a profit. The idea of giving a cut to ousters seemed like a bad idea. I'm not sure if it's changed. But when one considers the number of Etsy apps that have been made just for the joy of it, it would seem to be in Etsy's favor to incentivize developers once they can get the numbers to work out.