Affiliate marketing programs allows merchants to expand their market reach and mindshare by paying independent agents on a cost per action (CPA) basis. Affiliates only get paid if visitors complete an action.
Most affiliates make next to nothing because they are not aggressive marketers, have no real focus, fall for wasting money on instant wealth programs that lead them to buying a bunch of unneeded garbage via other’s affiliate links, and do not attempt to create any real value.
Some power affiliates make hundreds of thousands or millions of dollars per year because they are heavily focused on automation and/or tap large traffic streams. Typically niche affiliate sites make more per unit effort than overtly broad ones because they are easier to focus (and thus have a higher conversion rate).