There doesn't have to be a COMPREHENSIBLE way for the financial benefit to enter; there just has to be a PLAUSIBLE way (like Marxist economic theory: which doesn't have to work, it just has to sound convincing to callow college students.) And remember that internet marketing doesn't tend to attract the analytical mind or the veridical spirit. Pride ("_I_ am the foremost authority on, say, Christian Music"), envy ("there will be umpteen billion dollars of internet sales this year!"), mathematical ignorance ("Over 1500 ODP categories"??? -- and yes, in my family that IS one of the cardinal sins!), deceit in all forms (not least including the internet marketers who market internet marketing strategies to internet marketers on the internet, rather than keeping those strategies as quiet as was consonant with effective use of them, if, that is, they had any effective use.) ...
It is a heady diabolical mix. And it's no surprise that people snared by that kind of economic misanthropy often drift into acting on more generally malevolent impulses, and even cease to be able to recognize the existance of any other kind of motive.
The "directories" you notice are another symptom of the same pathology. There are lots of them, true. Most of them are simply one form of scam that the internet marketers run on each other -- you know, "buy a listing in my directory, and you will get better page rank than the ODP will give you--because there is so little competition in MY directory. Yet. But it will catch on soon!" So, sure, spend a hundred thousand dollars on a few thousand of these "classified ad farms" and ... that's another hundred thousand dollars that the internet marketing industry just made: selling that which not enriches the buyer, but makes us all poorer indeed. It's really not different from the new form of the old pyramid schemes, excuse me, "online networking" affiliate schemes.
It doesn't have to work. It never has to work. There just has to be a financial motive in convincing some small percentage of gullible people that it worked for you.