why not we call female friend or male friend?

I never really thought of that and I think your suggestion is a good idea. I remember when I was young I was always confused when people would refer to their female friends as girlfriends. I wasent sure if they literally meant they were dating that person or if it was just a friend. I still do get kind of confused about it so I always just refer to people like my friend Sarah or my friend Steve. If I was talking about dating someone it would be boyfriend or girlfriend.

To my knowledge and understand using 'female' word for a woman or girl is not a healthy substitute. Female has wide meanings and it appears bit derogatory and normally not used as a substitute for women or girls.

girl friends just means that you love the female,it is indiffenent from the female friends.