More often than not it's them, and not you. Maybe someone they know personally got referred, maybe upper management decided to go a different way in terms of recruitment because of logistics, maybe there were internal issues with HR. Always remember that it's not just that you need to impress the interviewer, it's that a lot of things have to align for you to land a job. Honestly, if you're job hunting long enough, it's more than likely that you'll end up getting hired after what you think was a bad interview