Maybe 1000 years ago, when "man" really just meant person and there was a different word for males in particular. Nowadays, to refer to people as "man" it just

Maybe 1000 years ago, when "man" really just meant person and there was a different word for males in particular. Nowadays, to refer to people as "man" it just sounds archaic and vaguely patriarchal, but people do it anyway because sounding slightly archaic can give your words more power.