It's sweet and it has a taste that many find pleasing and it's hard to copy exactly at home, that's the added value. You might as well compare steak with tofu,

It's sweet and it has a taste that many find pleasing and it's hard to copy exactly at home, that's the added value. You might as well compare steak with tofu, cinema with sitting in a park, playing videogames with playing chess. These things don't cost the same thing even though they arguably serve the same purpose. Some people might prefer one over the other. Saying that soda is basically water is like saying that going to the movies is basically like sitting in a park for two hours. Tap vs. bottled water is more perplexing because it's basically the same thing in both cases. It's more like going out of your way to go to a paying park instead of going to the one next door even though they're basically the same. I hardly drink any soda by the way, so it's not like I'm arguing that they have great value.