cf: https://en.wikipedia.org/wiki/List_of_Coca-Cola_brands https://en.wikipedia.org/wiki/List_of_Dr_Pepper_Snapple_bran... https://en.wikipedia.org/wiki/List_of_assets_owned_by_PepsiC...
EG: https://www.washingtonpost.com/news/to-your-health/wp/2015/0...
http://examine.com/faq/is-diet-soda-bad-for-you/ http://www.efsa.europa.eu/en/efsajournal/pub/3496
My favorite drink these days is the Dr. Pepper Ten...Diet Dr. Pepper has always been my favorite tasting of the sodas, but "Ten" purports to fit a good amount of sweetener in 10 calories...which to me, is just about as good as 0.
But yeah, I feel if they pushed diet sodas half as hard as they did regular drinks, the companies would eventually make a stable profit from it. But maybe it's too hard, institutionally, to purposefully cut into a profit center...in the same way that it was probably difficult for newspapers to try to compete with Craigslist because no ad manager would idly sit by and let his profit-making department be slashed.
Doesn't mean companies don't try though; in my city (Kraków, Poland) there were already several Coca-Cola campaigns trying to switch people to Cola Zero. One of them included disguising cans of Zero as regular Coke, attempting to show people that they probably won't even notice the difference if they don't know they're drinking a sugarless coke.