It's beyond me

I've been watching some of that The men who made us fat on the BBC. This week was about how people are getting fat on the healthy option.
In this house we assiduously avoid anything labeled with statements such as '30% less fat', 'Lite', or 'Now with fewer calories!' because we just know it is all bullshit cynically aimed at increasing profits. And guess what? None of us are overweight. Unbelievable.
Take Lurpak spreadable lightest for instance - they want to charge you for adding water - which is a pretty cheap ingredient - to their butter when you can just use the normal stuff but use less of it.
Why are people taken in by this crap? How?