I never understood why they stop communicating if an opportunity doesn't pan out? Why wouldn't they be interested in cultivating a long term relationship? That's what I think I would do if I were a recruiter. I'd keep in touch with say 200 people I know are really good and keep placing them as they switched jobs. I'm guessing at least 10 or 20 of those people would be switching jobs every year.
Because being good at your job would put you out of work. :-) If you place people into positions that they really fit with, odds are they would stay longer, ergo, less money for you. What you would need to do is sell yourself as an agent that is constantly evaluating new gigs for a monthly fee. I think that might actually work really well for devs that consult as a primary business.
It's speculative sure, but all long-term investments are.