Please note that we typically get many resumes for every position we have open. Even though you might have felt that you did very good in an interview, that may not necessarily be the case. Even if that is true, it is certainly possible that we found more qualified and/or suitable candidate for a given position. Obviously, no company hires every single person that they interview. You also typically attend many interviews and choose from multiple job offers. Some people whom we give job offer never show up to work. That is how the real life works. Many people memorize the answers but are not so good at coding and you must be one of them. I wish you good luck in your job search.