You're not likely to get it from the hiring manager or the people which interviewed you. However, if you went through a recruiter and have good rapport with him

You're not likely to get it from the hiring manager or the people which interviewed you. However, if you went through a recruiter and have good rapport with him/her, you may be able to get answers to your questions about "why" and what their reservations were. Whether or not this knowledge _actually_ helps you in the future is another, perhaps more interesting, question.