1.) Your resume is not targeted to a specific job/industry/organization.

Are you sending the same “generic” resume to any and all jobs/organizations? This is a big no-no.
Even if you are perfectly capable of being a Project Manager, an Accountant, OR a Logistics Manager, employers want the candidate who is eager to perform a specialized role. With that said, it’s perfectly acceptable to search for 3 jobs simultaneously, but you’ll need 3 different resumes.

Hint: in today’s competitive job market, resumes need to be tailored to specific jobs

2.) You’re only applying for jobs that are advertised online.

Are you spending several hours per day on general job search websites (i.e. indeed, monster, careerbuilder)? You’ll have a better chance of locating a job advertised on a niche or specialized job search site, and an even better chance by going to your target organizations’ websites.
However, you will have THE BEST chance of obtaining a job by using your network.

Hint: most people still receive their jobs through networking.

3.) You didn’t prepare for or present well at your interview.

Have you been on several interviews without receiving follow-up and/or an offer?
Your resume sparked interested, so you’ve already accomplished an important first step. Keep in mind that we do live in the Information Age, and therefore your interviewers already know a great deal about you before they see you in-person. Your job is to prepare for the interview thoroughly by researching the organization and key players, and anticipating how you can make a favorable impression. Be sure to practice interviewing with a trusted friend, colleague, or your career coach. Ask for feedback on your presentation and communication skills.

Hint: Ask yourself, honestly, why you’ve not been awarded an offer.