I doubt it has to do with scamming. I view it more as a cattle herder, with us being the cattle.
I'm a programmer and know a few programming languages. In my experience most of the recruiters just do "hey, Company is looking for someone with XYZ, this person says he can doe XYZ" and than refer.
They dont need to know what they talk about to get a decent recent. They'll never get a good result (unless by accident), but decent pays the bills.
They don't really need to match very well as it costs them a very minimal amount of effort to say "hey, here is a resume" and "OK great, let me push this button to send both parties an e-mail with a date/time". Basically a "throw it against the wall and see what sticks" way of working.
I know that the commission they get for a good programmer is around 10k-25k for most, so missing a few candidates, or having to send 5 candidates doesn't even come close to risking losses.
All they have to do is a "Hey, can I add your CV to the list?" and then to it despite your answer (because if you say 'no', but a percentage takes up an offer after they said 'no', that more money!).
I feel obligated to add that there are also capable recruitement agencies. But those dont have to scream so loud for your attention as they get word-of-mouth recommendations and referals.