I think knowledge surrounding healthy eating is so skewed. There are so many diets/ways of eating out there - Low Carb, low fat, slimming world, weight watchers, dukan, 5:2, paleo etc etc - that many of us have lost sight of what healthy eating is. Agree as well that portion size is an issue. I was really bad at this too, eating far too much even if it was healthy food. I'm doing SW, but even though pasta is 'free' I only have a handful and bulk out on veg and protein. The people I know who are shocked 1 pack of micro rice serves 2 (I used to be shocked too). My parents are guilty of this too - when mam makes a bolognese she uses 500g mince for 3 portions (no veg), I quite happily make the same amount make at least 5 portions by bulking it out with veg.
The price difference doesn't help either. A tesco value pizza and value chips is £1.75, a meal for a family and under 2 quid. A punnet of strawberries costs 2 quid, if you've got children to feed which will you choose? Fruit and veg are ridiculously expensive (admittedly apples and pears aren't but you'd soon get fed up of them) and it's a lot cheaper to buy crap. Add in the fact that it takes less time and energy to bung stuff in the oven and it's no wonder we're not eating the healthiest. I do slimming world and while I eat varied and healthy food (eg porridge and fruit, pasta in a creamy mushroom sauce with spinach and lettuce, vegetable fried rice) I wouldn't be able to do that if I was on UC. Supermarkets certainly don't help.
I work in a supermarket and they don't help matters. They have 'sweet free checkouts'. Yes, great except there's bags of popcorn, 'healthy' cereal bars, smoothie pouches etc. That's besides the fact that the end of the aisles facing the checkouts are adorned with pick n mix and chocolate. And that last month you could get 2 big pots of pick n mix for £3 wheras yet again strawberries and raspberries were 2 pounds. Which really annoys me, because working on the tills you could see parents saying theyre only getting them because of the offer, or that they hadnt realised they were on offer and now may as well get a second for free. Not very responsible. I think big retailers have a lot to answer for.
I admire food banks and often give (once every fortnight for example) and I understand they can't accept fresh things so happily pop in pasta sauces/passata/pasta/soup/cereal etc. At the same time I wish I could pop in something that really resembles a meal - a loaf of bread, bit of fish, some mince or chicken, some cheese, some yogurt etc. Understand it's not anyone's fault it's only preserved stuff they accept and it does make sense, but just wish there was another way
I don't judge but working the checkouts I sometimes feel sad. A mum buying school dress for her daughter, who she's told me is 6 next week, and while keying in the barcode as it won't scan, I see it is for age 10-11. Also seeing entire food shops that barely feature anything resembling a fruit or vegetable. I'm not perfect (definitely not), no one is, it does make me a little sad for the children though. Also aggravates me how the vouchers staff get are for money off salmon, chicken, water, exercise equipment and salad, yet the customers get money off aunt bessies steamed pudding or ben and jerrys ice cream 
Time is a problem too. I've started cooking easy meals when I get in from work (chicken and rice and veg, stir fries etc) but I work in a sedentary job. I rarely work longer than 10 hours, and even if I work 10 hours I get 2 half hour breaks so enough time to eat food I've ready prepared. I live 15 mins from home, my jobs not very stressful. That's not the same for everyone. Some people are shattered emotionally and physically after work, some work long hours, some have long commutes (esp. in cities). In those cases it's perfectly understandable reaching for a pizza/ready meal in the shop on your way home. Time is a big problem I think, we all spend so long doing other things that healthy meals take a back seat. I know you can batch cook (I do) but that again takes time and effort. I don't know what the solution is, but there is a problem. I think education is the way to go but that still causes issue - I'm 22, living at home and trying to eat healthily in my house is difficult sometimes. Let alone if you're 13 and know from school what you should be eating, but your parents won't listen and you can't buy the other food for yourself.