Actually, it's that damned sugar support price.
Confectioners in the USA have to pay approximately twice as much for sugar than confectioners outside the USA due to the federal government's dumbass support prices designed to prop up the few cane sugar producers in the country.
The price of sugar is not why auto plants and parts plants and every sort of plant anyone can name went to Mexico. Cheap labor is what lures most plants from the US, and it's a major factor for candy and other producers that uses sugar, also.