There are so many affiliate program on ineternet.People at first got attracted to this affiliate program but later when they got ,you have to sell the product for which you will earn money.It was hard for them to earn money quickly.As there are so many scams going on interenet ,people not easily buy those products.But once you sell a single product the income was more.Later the pay per lead program was came into existence.Where people give there referral links to other people and if those people singup with that that referral link then he will earn money from that lead.People then started using chatroom to find people and tell them to sign up as there referral and then can earn money.People who started first earned a lot but once most people got those things people never signed as a referral for that person.
Then google adsense started pay per click program which let them to earn money when someone visit there website and click on google ads.If they don’t click on there website then it was counted in terms of impression.The earning for pay per click is less related to other pay per lead program.But chances of people clicking on google ads was more as google would display ads related to contents.So most people started joining google adsense.