There will people who only buy stuff based on price or alternative cheaper brand but for many, they usually pay extra for brand and the taste they like etc.. especially something as cheap as coffee or coke, it a little luxury you can enjoy without breaking the bank.
Long before I own Coke stock, I only like coke and willing to pay a bit more for it, I don't drink a lot and I prefer coke over anything else and I am willing to pay a bit more for it.