Why most HR personnel in companies are women and few men?

I am a social psychologist. There is not 1 reason for this, but it's the end result of the combination of many aspects. First, there are many families and school teachers promoting boys more than girls in playing engineering & math related toys and doing such activities, while girls are promoted to participate in more interpersonal activities such as playing with each other's dolls etc. Then, about high school age comes the selection bias. Boys are self-selected to more math&engineering related education paths and girls to more verbal areas such as psychology, literature etc. In the end the job selection that's suitable for their educational history differs, when they become young adults males do start engineering related jobs more often and females do start interpersonal jobs more often. There is more factors to this phenomenon but the text would be too long then. You can have a search based on this information to discover more to the concept.