Why do large companies appoint managers with no human resources experience as their top human resource executives?

I don't believe this is true. What would be the point in being in human resources if you had no experience with the position.

Hiring non-experience managers happens in any department. More likely they do have degree in business. HR has many specialties and it would be very difficult to be an expert in every area in HR. Within the HR department you will probably find that he or she has the support of technical experts to rely on for information or guidance to make good sound decisions. HR is a people driven area and if you have common sense, support of specialist, support of legal experts and especially are a compassionate caring person you could manage just fine.