Many recent studies have found incredibly high numbers of obese children in the US, and parents have taken a hard look at their kids' candy intakes.
Many manufacturers had made small lines of sugar-free candies in the past for diabetics. The companies had not realized that non-diabetics might appreciate having candy that was free from sugar. Once the manufacturers began paying attention to the greater market, sales skyrocketed.
Hershey's, for example, makes the sugar free Reeses peanut butter cups that I adore, and that combine delicious taste with zero sugar. Gummy bears and jelly beans are other candies that taste just perfect in a zero-sugar lifestyle. With candies these good, why would someone eat the sugarred variety?
Those in the industry see the trend as continuing and becoming permanent. With sugar causing cavities and weight gain, and candy being a 'treat', it makes sense that treats become a less impactful part of a daily diet.

Lisa Shea's Library of Low Carb Books