Three common artificial sweeteners, namely saccharin, aspartame, and acesulfame, are now in the public domain, patents long expired. Big Sugar can do nothing to stop them. How could stevia make things any worse for Big Sugar, especially if it has a problem with aftertaste? This is like the way the dairy business got margarine advertisements banned from saying anything about butter.
There is big sugar/food industry, then there is big chemical industry, like Monsanto (NutraSweet), who are in the sweetener biz. Since Splenda is manufactured from sucrose/fructose it is not a "chemical sweetener" per se. It's a big profit-maker for the sugar/food industry.
Stevia is a problem because it is natural and renewable, and cannot be patented like a man-made sweetener. The lack of access keeps the price high, but if it were approved the price would plummet and it would be very competitive. You can't turn your garden corn into fructose, but you can grow stevia and pluck the leaves for direct use.
As far as the taste, there are a few brands that are already perfected to the point of virtually no aftertase.