The truth is that very few interviewers are ever trained for the role of interviewing and recruiting employees. This aspect of working life is more of an art than a science. The ability to interview people with a view to hiring, is a skill that is acquired over time and, like with anything else, will involve a few mistakes along the way. As the old saying goes, "good judgement and good experience comes from times of bad judgement and bad experience."
Interview candidates expect that the people who will be interviewing them will be far better organised, more experienced and know every trick in the book about everything. This is far from the truth. Often the people involved in making appointment decisions are not used to having to do so. For many interviewers, having to conduct an interview is seen as something of a waste of time. Inexperienced interviewers are sometimes even more nervous than the candidates before them.
It tends to be only with the larger companies that there will be many people involved in an interview with most of them having had some time to prepare for conducting an interview. Smaller companies will naturally have fewer people involved, but this doesn't mean that the interview will be any easier. One experienced interviewer is worth five inexperienced interviewers. Unfortunately, irrespective of an interviewer's experience, they will nevertheless deliver their opinion of you. You will obviously need to win over every interviewer regardless of their level of experience.