there is not any real difference in production cost..you could argue that the economy of scale enjoyed by the 'proper' premium brands, coca-cola / pepsi negates any marginal difference in raw material cost
with a premium brand you get consistent product that you like the taste of
coca-cola has one of the biggest global marketing budgets especially sports event related and this keeps it at number one and still leaves a very sizeable excess margin for discount promotions
other products are perceived as inferior and i personally would agree even to the point where i have argued about even coca-cole corps attempt to convince us that low or lower sugar/calorie versions are equivalent.....
coca-cola zero does not have 'the great taste if coke' it is horrible and even worse that that gutrot diet coke
its a free world just, if you want something wet drink water.....if you want an alltime classic beverage it is original coke with the small exception in a pizza hut when pepsi is acceptable