It sort of is our own fault and sort of isn't. By that I mean we have a food industry who's sole purpose is to cause addiction to unhealthy foods. Addiditives such as high fructose corn syrup (which is in everything now), MSG, and others offer nothing to the body except fill it with empty calories which causes a nutritional starvation. The fault is on the individual to realize this (hey, look I put on 10lbs this year, i'm getting fat maybe I should stop eating shit) and take action.
We've also moved from working outside and doing a lot of manual labor into office jobs sitting at a computer working 8+ hours a day and having a sense of not having enough time so the quickest source of nutrition becomes the worst option available.
Processed sugars, MSG, Aspertame and the like are all part of the scam by the food industry and should be avoided at all costs.