Nothing is missing, it's just a bit of an upfront cost if you want soda that doesn't taste terrible. All of the consumer products are cheaply made, weak, and ridiculously overpriced even for the terrible quality you get.
If you want something that tastes as good as a restaurant then you pretty much need to buy the same equipment and it'll set you back at least $1k^, a weekend projects worth of installation time, and the cost of a CO2 tank and bulk syrup.
^ You can probably get under $1k if all you want is a soda-gun without the fancy dispenser.