The best way to think about affiliate marketing is quality over quantity. There are a lot of small websites that will promote your product, but the key is finding a small number of partners that will deliver conversions. For example, an equity management services firm has over 20,000 affiliates in its system, but only about 25 affiliates generate 85 percent of revenue.
In the case of cost per mille/click, the publisher is not concerned about whether a visitor is a member of the audience that the advertiser tries to attract and is able to convert, because at this point the publisher has already earned his commission. This leaves the greater, and, in case of cost per mille, the full risk and loss (if the visitor cannot be converted) to the advertiser.
If my piece of content is so unique and valuable around hiking backpack recommendations, that other reputable outdoor websites are willing to link to it and build the page’s authority, then I’d have a very real opportunity to rank high in organic search for these search terms (meaning, my page will come up first when someone searches for hiking backpacks).