Why was Prince Louis XVII Dauphin of France, son of King Louis XVI, basically tortured while in prison?

I am very curious as to why this little boy was tortured while he was in prison away from his family. I know his father Louis XVI died in January of 1792 and his mother died in October of that year and there was no way they could help even if they could. I also know that he died while in prison due to neglect. So all in all I was wondering why this young boy was tortured; was it because he was the Dauphin of France and could at a later time reclaim the throne of France or not.