Hello Michael,
Thank you for posting your question. It happens more often that one would expect. Lack of transparency and feedback from recruiters both internal to an organization and external.
First and foremost don't be frustrated. Keep in mind that a single individual that posts a job position may get hundreds of responses. Sending out that many customized denial letters probably is not feasible, that is why they send out generic ones.
Also, don't leave the job of what aspects of YOU didn't work up to others. There are two elements to getting selected. The first is, do you have the skills necessary to do the job. The second, is your personality a good fit for the culture of the organization. The flip side of that is, is the company a good fit for YOU! Don't get stuck in making a move because the job looked good on paper only to find out it is a terrible fit culturally.
If the "Job" is something you really want then keep developing the necessary skills to do that position well. Certifications, professional associations, back to school, internship, whatever it takes. It won't be easy, but doing any of these things helps improve your skills and in turn makes you more marketable.
I agree...I wish companies and hiring professionals did a better job of giving constructive feedback. But remember, their job isn't to give you constructive feedback, it is to find one candidate that fits both the job and the culture well...
YOUR job is to prepare yourself, keep a positive attitude, take what feedback comes and to continue to develop yourself.
I hope this helps and feel free to post more questions if you have them!