I think, and this is just a theory of mine, it is because they are paying the owners of the site. Put yourself in the shoes of the asshole who works at the marketing division of a fake pot company. Where are you going to advertise your product? You're going to try to go for the pot smokers since nobody who isn't a pot smoker is going to even consider buying the product.

Now put yourself in the shoes of the website owner. You need some revenue from ads, but no company wants to be associated with dirty druggies...but wait, these fake pot people are offering me boatloads of cash!

And that's how they get more gullible 14 year olds to flush their money down the crapper.