Everyone likes candy sometimes, right? People make money selling candy. Why don't spammers sell candy?
It seems to me that you would expect spammers to be proficient, on the whole, at what they do. You'd think that spammers would gravitate toward better and better propositions. For example, if you make more money selling candy than imaginary drugs, you'd expect in time to get more candy spam and fewer fake drug ads.
Why don't we have spam for hit music? Everyone likes music. Why don't we have spam for cleaning products? Everyone has dirty dishes.
What makes sense to spam? I'd say, products that almost anyone might want, but that aren't trivially available at local brick-and-mortar stores or high-profile, legitimate Web dealers. SPECIAL candy, for example -- either really tasty candy, or candy for diabetics, or retro candy with nostalgic brands, or candy at great prices. SPECIAL FOOD INGREDIENTS would work too: truffles, dried mushrooms, spices that your local store doesn't stock. ART should work well too -- stuff for your wall, stuff for your screen -- stuff you want. CUSTOM EROTICA, which has always supported some fine writers, should work as well.
But, somehow, people seem to do better with snake oil. I don't get it.