People like to think that they got selected due to the quality of their application compared to others. Most underestimate the amount pure luck that is involved in being selected for an interview at any company since the quality of the applicant is the same at United, Delta...... A friend of mine was 21 year O5 in the Air Force, instructor pilot, Air Force Academy grad, Masters in aeronautical engineering, community volunteer work, and tons of internal recommendations. He ended up at Delta, but never heard a thing out of the other airlines that you listed. He got lucky, but United was his first choice due to the Denver base and he regularly updated his application for a couple years before giving up and settling in.