I have done this myself and the answer is usually that they found someone with more experience, non-personal. Recently, I got feedback that they thought that I was someone that did not handle stress well. I have military experience, I love stressful and complex problems. I wonder if my stutter caused that line of thought. I've done what I could to not take things personally since a lot of non-stutterers seem to also have issues finding the right job fit. I have found that self-disclosing my stutter before interviews has really helped with lessening disfluent moments and having recruiters assume things about my personality.