There are quite a lot of zero-calorie soft drinks on the market. Diet, zero, the companies brand them with different things.
I don't know for the most recent ones, but diet soft drinks usually have aspartame to replace sugar.
The problem is aspartame:
1. Tastes crappy
2. Is presumably cancerous
Now imagine if they found a sugar substitute that would taste EXACTLY like sugar, would have zero calorie and would induce no damage to your system (cancer-free).
In other words, you get the same soft drink, minus the diabeetus* and other problems related to carbohydrates.
Would you buy/drink it instead of the regular one? Would the regular one be discontinued because people would all switch to the calorie-free one?
*Correct spelling is diabetes