I agree wholeheartedly! The availabilty of cheap energy dense foods which are high in calories is a major factor in the increasing obesity problem seen in western countries. The other factor you mention-decreased exercise for many with desk-bound jobs is also important.
The only solution I think is to educate people to eat a healthier diet and take more exercise. These are probably as important as not smoking tobacco or drinking too much alcohol in order to maintain a healthy active long-lived body...