Why is it illegal to purchase Jack Daniels whiskey where produced?

It is not illegal to purchase Jack Daniel's whiskey where it is produced, which is in Lynchburg, Tennessee.

You can buy Jack Daniel's whiskey at the Jack Daniel's distillery in Lynchburg and at various liquor stores in the surrounding area.

There might be some local regulations regarding alcohol sales, but it's definitely not illegal to purchase Jack Daniel's in its place of origin.