Because they pay good money. Done correctly, a site can sponsor itself, servers cost money even if you are nonprofit. As for the affiliate sites not being listed in directories, it depends on wether you site has content or is just a doorway with a link to the affiliate programs. The only ones who don't want affiliate programs are the big, mostly dead now, etailers that have been taken down by the little guys with affiliate links. One rule of thumb I use is to never offer more than 7 and preferably only 3 affiliate links that absolutely correspond with the sites content for each page.