ehh...It's a business. If women, all of a sudden, stopped being a large consumer of diet soda, I guarantee you, whatever they wanted instead, would be the primary focus of the black widow/Potts ad gimmicks.
To be some vast, oppressive conspiracy trying to keep women down, at this point, would mean they would offer nothing but diet soda, no matter what the consumer wanted. No one who wanted to stay in business would do that.