This makes me angry.
The reason that health professionals focus on diet and physical activity is because science evidence demonstrates that these have the most positive impact on long term health. The majority of healthcare (inc. social care) spending is on reactive and emergency services. We don't spend anywhere near enough on preventative healthcare and interventions. Tackling social factors (providing education/access/choice) could go a huge way in reducing obesity, increasing physical activity and improving health. Let's not discount it before we have actually given it a go.
People need to take responsibility for their own health. We don't need another excuse to justify why you are fat. We need to provide people with the knowledge and access to make an informed and active choice about their lifestyle.
*edited, realised I had re-framed a sentence without correcting the beginning of it.