Because they either do that, or sit and spin in some far off corner of the map. I don't know if it's SAIN alone, or a combination with another mod. I tried to make sure that wasn't the case, but I could have missed some checked box somewhere or a true/false boolean in the config code.
If you do not have Looting Bots or Questing Bots installed this may be part of the issue, as without these mods bots will tend to only really stay in one place and react to sounds near them.