Is there a reason for why Im the only one in my entire family tree who stutter ? and mine is even severe

Is there a reason for why Im the only one in my entire family tree who stutter ? and mine is even severe I have seen some people here who say that they have a family member who has a stutter and they inherited it from him/her but what about people who don't have a single person who stutter in their family tree ? what could be the reason behind it ?