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.
'They' are actually robots. In my experience they never stop communicating. Once you are in the database, they'll spam you forever.
In my experience, that works well. As does, "I have N years left of graduate school and will not consider other opportunities until that is complete."