It is not instinct, it is a habit. Your question is phylosophic: "Why languages are different?"

Pure reflexive normally doesn't make any ambiguities when building phrases, so it is good enough. Replace in English words like myself, yourself, himself by just self and you'll get the same. -self always refer to the subject, and so parts my-, your-, him- in fact add no information (they are tautologies) and can be skipped.