The enormous cost of these drinks is what principally drives the soft drink industry. Not health of the customers.
They take a tiny proportion of natural ingredient..fruit juice...and then add water, to make it look and taste full strength they then have to find the cheapest possible additives to colour and flavour it. One reason for using artificial sweeteners is that theoretically and in the eyes of the consumer sugar is bad for teeth, but also..
Sugar is cheap. It costs about 6p to sweeten one litre of soft drink. But some artificial sweeteners are even cheaper, costing only 2p or 3p to sweeten one litre of drink. You might expect to pay less for artificially sweetened drinks, but most manufacturers sell their sugary and artificially sweetened drinks at the same price.
There are only a few artificial sweeteners permitted in foods, and these are restricted to certain uses. Acesulfame-K (E950) and Aspartame (E951) are 200 times sweeter than sugar. Saccharin (E954) is 350 times sweeter than sugar. There's also a new sweetener starting to be used in some foods and drinks, called Sucralose.
In the case of fruit shoot having made it from a tiny amount oif natural fruit juice they then add vitamins to give it a healthy image. This is because drinks perceived as unhealthy are experiencing declining sales and juice drinks sales are increasing.