Yes, there are genetics at play here. Probably lots of them. Different people reacts differently to various food. As a GENERAL rule, I'd say fast food is bad while activity is good.
I suspect that in 10-20 years there will be a menu based on your DNA.
There is also a problem between the ears. Talking to grossly overweight people about their weight is like speaking to smokers about smoking. Essentially, they'll skirt the issue with lots of good humour, feints and every dodge they can think of to get away from the theme.
We tend to run away or attack what we don't understand - and commiting slow suicide is definitly something we all would have difficulties with.
Also, losing weight takes time and dedication. Modern times is all about quick fixes. If you tell anyone you need more time than five minutes to make things right, they'll walk away in a huff (of course a completely unknown situation to anyone in IT-Support )
A third element is the commercial one. When you walk in to a food store, what are the first products to meet your eyes? What do people in films and television eat (and stays slim)? What food is prominent in advertisments?
I find the topic interestning since I've idly (touché) been trying to get rid of a few extra kilos/pounds for a few years. Once I keep strickly to the "good menu" (which agrees quite nicely with my digestion) AND uphold a high level of physical activity, the fat starts slipping away over a month or two. Once I stop paying attention, it creeps back. Well, I keep trying
Citrix:
Next time some flight attendent start fussing about my overnight bag being "overweight", I'll close the argument by just directing attention to the nearest whale