The problem with Stevia is that the crude extract has a number of different glycosides many of which have a bitter aftertaste.
Only one of them called Rebaudioside A is considered acceptable.So to make use of Stevia there must be factories that can isolate Rebaudioside A from the plant.It is not something which you can grow and use all by yourself unless you dont mind the bitter taste.
However it can be a valuable cash crop for cultivators.