Why is the Gastric Band on the NHS?

I disagree with gastric banding on the N.H.S but the logic behind it is that fat people cost the N.H.S more long term. So, if they can deal with the fatness now and spend however much on the op then it is better than spending even more money later as they become crippled by their own fatness! So many times I see people in my local supermarket car park heaving themselves out of their disability vehicle with a cig in their mouths and huffing and puffing about how hard their life is. Overeating is a life style choice like drinking and smoking. I do all three so I am not the saint here. However, I know the difference between a treat and excessive greed. If the people that want a gastric band are prepared to risk their lives on an operation why won't they risk a healthy life style first?