I just finished a long job search and I had this happen to me many times and I know I'm a good candidate. In most cases, the recruiter's pay is dependent on successfully placing candidates...in volume. So for a lot of them (not all) anything that doesn't contribute to placing candidates isn't worth their time. Plus, they are calling you back to give you bad news, and they might have sent 5 or more resumes in for a single position so that's at least 4 people they have to deliver bad news to and they are usually have lots of open positions on their desks. Let's face it: it can be an awkward call. "Hey, Tim76." "Yeah! Did I get the job?" "No..." "...OK"
At one point in my recent job search I was getting really depressed...until I realized what was going on. I would spend 30-60 minutes talking to the recruiter before he submitted me. We would spend that whole time talking about how to market me for the position, why I was the best candidate, etc. I would get myself all psyched about how this would be a slam dunk. Then I wouldn't hear from the recruiter for a week... Once I figured out that I needed to be a lot more leveled in my expectations, there were a lot fewer highs and lows in my job search. It all became routine.
Also, from the recruiter's perspective and depending on the industry (I'm in software development which is still hot despite the current economy), people might not be on the market that long so a lot of the recruiters expect that you'll get picked up by someone else before they have another suitable position cross their desk. So again, there's not a lot of incentive for them to invest time in building a relationship with you.
There are a few really good recruiters out there, a lot of mediocre recruiters, and way, way, WAY too many really bad recruiters. I kept a list of the recruiters who spent time asking me what I was interested in, who called me back even with bad news, and who called me to ask me for advice on issues that were completely unrelated to me. Those are the recruiters I'm going to call first next time I'm doing a job search. Half of them probably won't be recruiters next time I'm in the market. And of the ones who are, they might not be the ones who find me my next job.