You can divide the population into three groups. First there's a minority who eat well and exercise, they're not a burden on the NHS because they're a minority, and they are the healthiest.
Secondly, there are a minority who can't exercise, they're still not a much of a burden because they're a minority even though their needs may be complex.
Lastly, there's the majority who eat poorly and do no exercise from choice (or at least it was a choice before they made themselves ill). It is these who are the burden, both because of their numbers and because they are less healthy.
There are plenty of healthy options in most supermarkets, but the quantities they stock reflect the quantities they sell. The reason that there are many aisles of junk food is because that's where most of the trade lies, when people change what they buy the shops will change what they stock. You can't expect them to have junk food aisles that are all sold out and piles of unsold fruit and veg rotting. Supermarkets adjust their stock to match sales, not the other way around (a common reason for discounts is when they misjudge demand, and have a surplus to shift before it goes off).
