HFCS is used because it is cheaper due to subsidies. I think HFCS will be removed from most sodas in the next five years because the producers know it is causing health issues. Most grocery stores in my area have Pepsi's three main products (Pepsi, Mt. Dew, and Sierra Mist) available without HFCS. Of course they are marketed as "Throwback" or "Natural" but I think they know HFCS in soda will be a PR nightmare in the next few years.
In my area you can also buy Coca-Cola imported from Mexico that is HFCS free.