Well, there are, of course, a number of reasons, but perhaps the primary reason is because we're still organized as a species in the same way that we were organized 200 or 300 years ago.
もちろん 多くの理由があります でも 恐らく一番の要因は 人類は 未だ2, 300年前と 同じように組織されている ということでしょう