Even that doesn't quite make sense, because there's 80 ingredients in there, and if you're only ever drinking 3-4 drinks, you probably won't use a large portion

Even that doesn't quite make sense, because there's 80 ingredients in there, and if you're only ever drinking 3-4 drinks, you probably won't use a large portion of that cartridge. Right now, you get the cartridge for free but pay basically for what you use. You can think of it as paying for the part of the cartridge you use (the drink), and they recycle the unused ingredients when you send it back to them, refilling it for free.