There could be many reasons for this. Keep in mind there are normally thousands of applicants for a job and the hiring managers will shortlist only a few candidates. If you didn't hear anything after a month or two, it's safe to assume you didn't get shortlisted. Hiring managers do not normally send out regrets. Keep in mind that since this is very competitive, make sure you aply to jobs you are truly qualified for and meet all of the job requirements. Also make sure your resume is well written and easy to read. Hiring managers only look at it for a few seconds, so you need to do what you can to impress them in only a few seconds.