Because code of conducts makes it easier to harass people. If there are formal rules then all a harasser has to do is to find something out of context and then start harassing the person by starting a CoC breakage investigation. Doing stuff like that without a CoC would get you kicked out.
Not neccessarily. Usually that's a new "exception" to the formal rules. (This happens anyways with more generalized rules.. but that's done under the spirit of the rules and is accepted as such)
Because code of conducts makes it easier to harass people. If there are formal rules then all a harasser has to do is to find something out of context and then start harassing the person by starting a CoC breakage investigation. Doing stuff like that without a CoC would get you kicked out.