For economic reasons, home soda makers have mostly standardized on a very concentrated range of 20:1-25:1 syrups where most of the water comes from the tap and as much as 24/25ths of the bottle is carbonated tap water, the syrup is strong enough that only a small amount is needed for flavor. Commercial syrups are typically 5:1, meaning you only fill the bottle 4/5ths of the way with water because the rest will be syrup. That’s an awful lot of syrup used for each drink.

The problem is it’s very hard to concentrate sugar-only syrups to that level without triggering crystallization of the sugar. So they mix artificial sweeteners to make it sweet enough without using so much sugar. Commercial sugar-only syrups like Coca-Cola are far more diluted (ie, they contain significantly more water) which means they are larger and heavier for shipping and stocking and get used up much faster since they require more syrup mixed into each drink.

There’s nothing technically preventing you from using a commercial 5:1 syrup, other than that it’s less convenient. The main problem is it’s very difficult to find since there’s relatively little demand and the commercial soda companies keep it pretty tightly controlled through their distributors.