Here's where you and I diverge:
1) Yes, engineers and other in-demand workers have ready access to jobs. I remember when I was looking for a good engineering job out of Amazon, I was basically spammed nonstop by virtually every party on the planet.
2) But the opportunity cost for poor job selection is enormously high. The difference between choosing between a good startup on good terms, and a less-good startup on less-good terms, can literally mean the difference between retiring 20 years early having your work used by millions of people, and just puddling around for a few years with, say, the occasional PyCon lightning talk for visibility.
At http://offerletter.io , we are doing precisely this - we are getting paid by engineers, designers and PMs for value added - in this case, during the negotiation process. Our team of Advisors guides candidates on the "last-mile" of offer selection and negotiation in exchange for a cut of the increase.
It makes too much sense - there's massive information asymmetry during the process, companies are full of shit, and many people outside of "the club" - however you choose to define it - just don't know what they're worth, or how to get it. While we can't justify charging the $10k-$30k that recruiters make, the incentives are still incredibly strong for us to do what we do.
And of course there's the ethical and human component, which is very strong - I tried more traditional recruiting for a while and just raw selling of companies is so tiring. I like helping people first - all of the Advisors do.