Why do they do this?
Sure, with the stuff they add to replace fat and sugar they may make it less healthy, but the fact is, they market to uninformed people.
No, they don't market to health nuts, but they market to moms. Most moms don't really know what things are good and what it bad, they just look to please there kid. When they see, "Propaganda'd X free" they decide that is a healthy choice which makes it even better.