Is this because WP is now blocking outside adds on free accounts? WP recent advised users that ads may appear on free accounts. I saw that WP has a plugin just for Amazon posts, but any plugin requires a business account. In looking at the pay-to-play WP account details, it looks like one has to buy the second level account in order to “monetize your website”.
Affiliate networks offer you access to multiple (and by multiple, we mean hundreds if not thousands) of individual affiliate programs. They basically work by simplifying the signup process - instead of applying to become an affiliate for a each product you want to promote, you simply apply to join the network and instantly have access to hundreds of different affiliate offers.