There could be countless reasons why a person is not getting hired. Their experience or educational background do not match the job requirements, their resume is not impressive, they're not interviewing well, they lack quality job references, their personality is not a good fit for the existing team in place, didn't dress professionally for the interview, smelled of cigarette smoke, was late for the interview, made some off color or unprofessional remark during the interview....etc
There are a million reasons why a person doesn't get hired. However the most common reason is you were not the most qualified candidate to apply, someone "in-house" got the position, or the company decided to withdraw the position altogether.
Instead of trying to figure out why you're not getting hired focus your attention on how to get hired. I know it sounds like word semantics but one is looking for the negative and the other is looking for the positive.
There are several books out there one can check out from the library or purchase from Amazon or wherever to polish up their resume and interview skills. My favorites are a couple of books by Martin Yate.
"Knock 'em Dead Resumes: How to Write a Killer Resume That Gets You Job Interviews"
"Knock 'em Dead Job Interview: How to Turn Job Interviews Into Job Offers"