Good point. Companies can only sell those products for which there is demand. In Pakistan (as compared to the example you give for Canada), many prefer regular sodas with sugar over diet or other alternatives by choice.If Pakistani consumer tastes change, Coca Cola will make healthy drinks.
E.g., in Canada, both Coca Cola and Pepsi are competing for the scented carbonated water with Aha! and Bubly, respectively. Heck, even Pakistani companies can get on this market since it's relatively open still. Someone needs to make 'pop pani' in Pakistan.