Artificial sweetener

Grr–I used to be able to avoid nasty artificially-sweetened drinks by avoiding anything with “diet” or “lite” on the container. But in the last few weeks I’ve been suckered into buying some Fanta variety powered by both sugar and artificial sweetener, and this afternoon I mistakenly bought some Marks and Spencer cordial sweetened the same way! Why are companies doing this? Is it because artificial sweetener is cheaper? (Sometimes they’re advertised as being “low in sugar”–there was an Apple-flavoured Fanta advertised like this–but most of the time it’s not noted on the bottle.)