Low fat may mean low fat but it covers up the fact that people don't really like the taste of low fat. Try feeding skimmed milk to kids, they don't like it. That means they replace the fat with high sugar - which is worse for those eating it and a flavour. They then extol how the calcium and low fat content is good for kids. It is a lie by omission, which isn't covered by the ASA. I could put a low fat statement on a 2 kilo bag of sugar.

The companies gain because sugar, of any kind, gets mass produced and is really cheap for them. They have no reason to do otherwise than pack it in. Sugar affects people's eating habbits, it gets digested very quickly, stops people feeling full and encourages them to eat more. That means corporates have absolutely no reason to change and every reason to promote eating sugars.

If they wanted to be truthful they would put a big sticker on HIGH SUGAR - THIS PRODUCT WILL MAKE YOU FAT. They don't want to be truthful, it is against their shareholder's profits to be truthful. Corporate management can and has been sued for doing it by their shareholders.

Not sure where you are buying your low fat diet foods but normally you'll find they use sweeteners not sugar in its place.