The dynamic that is at work here is very much like what was done by William Randolph Hearst back in the 30s to get marijuana made illegal.
I don't doubt for one second that efforts by those who produce artificial sweeteners have something to do with it.
But then, I'm about as cynical as they come.
Two words: SUGAR LOBBY
Sugar in other countries is very cheap, but in the U.S., it is subsidized. The price is higher, making it less attractive for candy and pastry manufacturers. The sugar lobby has brought sufficient pressure to bear on the producers of stevia products to prevent its designation as a food. In the case of Nutra-sweet, the formula was purchased by one of the major food manufacturers in order to prevent it being used in competitive products without licensing. Perhaps someday, this will also happen to stevia. But as long as the sugar growers have any power, they will do everything they can to prevent it.