If much of the population is obese, or doesn't exercise, or drinks to excess, or smokes, or takes drugs and if there's isn't safe effective care for people leaving hospital, all the quality improvement in the world wont make much difference.
I think you are confusing public health with quality improvement.
In fact it goes beyond public health remits and into deprivation and poverty, an increase in which is due to austerity and the continuation of policies that are to the detriment of the working classes.
Properly funded public services can provide support for people wanting to lose weight, stop smoking and come off drugs. Unfortunately we don't have them anymore so those services are decimated and people can't get the help and support they need to improve their lifestyle and health.
The scary truth, however, that many people on here seem to ignore is that obese people, smokers, drinkers, hell, even drug addicts all,pay into the NHS too and so are as entitled to use the services as those among you who break bones cycling or ski ing.
Quality improvement is a process by which small changes in processes and pathways are identified and implemented by staff working in those services. In my long career in the health sector, I've found that given the time, headspace and trust, healthcare staff (clinical and non clinical) are very very good at improving their services. Fancy that.