One of the biggest factors contributing to obesity is the ease by which unhealthy diet choices can be made compared with the relative difficulty of making healthy ones.
Healthy options tend to have at least one of two major drawbacks: they are expensive and/or they are time consuming. On the prepared meals front, the healthy ones (like kashi) are always more expensive. Even when they are affordable, there are still plenty of cheaper options. Organic complicates this further. Much of the organic labeling doesn't really matter, but in the places it matters most: meat and dairy, it is the largest price jump on the most expensive items.
It has come up here before, but eating healthy is not necessarily expensive, it can, in fact be quite cheap. Trouble is it takes time and effort. And I don't mean just the prep and cooking, as there are plenty of meals that are very fast on that front. What I really mean here is the planning and forethought. In order to get a meal together, you have to decide what you want to make, ensure that you have all the ingredients (or go to the store to get them), and then get them out and start the prep. If this is for dinner, then it could be after getting home from work, and when you are hungry and not really in the mood to think about cooking, but just wanting to eat.
There are all sorts of ways to get around that, but there are always trade-offs. You can make large meals on the weekend, then box up individual lunches/dinners throughout the week. But this means giving up weekend time for cooking, and not everyone wants to make that trade, and it also means not having day to day choice. Now having choice really is a luxury, but it is one we have become accustomed to. The ease with which we can order pizza, or grab a burger, or even pick up the frozen meals at the supermarket is remarkable by comparison.