Eating less is cheaper than eating more. Drinking water instead of sugary drinks is free or cheaper, assuming you avoid bottled water. Walking more is free. Running is free.
Instead, the things you see advertised are: big meals, value for money eating, exercise equipment, gym memberships, soft drinks, juices, supplements (my god, the advertising of supplements in Australia is insane).
And so, because of the onslaught of advertising, people think the ab-roller is going to eliminate their gut or they're tempted by the advertising of treats or "healthy" juice and so on.