There is no systemic institutionalized anything that prevents someone from shutting their phone off and going for an hour walk a day. Or buying chicken breasts and cucumbers, peppers, and tomatoes that cost nothing and can be cooked on a $30 George foreman grill.
Most protien heavy fresh meats are very cheap, and most vegetables are cheap as well. At least as cheap or cheaper than an equal quantity of sugary snacks or crackers or pasta. And certainly cheaper than frozen meals or eating at a fast food place.
I say this as someone who is overweight and has struggled with it since being out of college. My fitness pal is free to track calories, going for a walk is free, and simple healthy food with non-salt heavy seasonings are cheaper than most unhealthy options.
If you don't have motivation everything else is irrelevant. A team of specialists could make it it's personal mission to get you healthy but you need motivation to make it happen.
There's also some recent studies that believe that the types of food we eat enable certain types of gut bacteria to thrive on that type of food and send signals to our brain demanding those types of foods more.
That means if you eat healthy, your brain will want healthy foods. But you have to break that cycle first.
Ok, so how to get people motivated to do all these things?
I think you've scratched the surface here a bit, motivation. The question is why do you need special motivation to be healthy? Isn't that a clear indicator of an unhealthy living environment?
I'd like to make an example of your first point. Yes, nothing (outside some health related factors) is not preventing you from going to a walk and nothing is preventing you to buy healthy food and cooking it. But the thing is it's much easier to not do all these things. One factor driving the crisis is the convenience of making those choices.
In terms of physical exercise, in modern world, it's increasingly becoming something that you have to do on top of your daily schedule instead of something that happens in our everyday lives naturally. I'm talking about how we get around. There's something really wrong about the idea that you have to drive to a gym to have physical activity or especially needing motivation to walk, which is one of the most natural things for humans. In a well built environment that happens almost automatically as you can walk or take transit from a to b.
Now take the food. It's not hard to understand why people go for processed foods instead of fresh produce. It's not all about money, but the convenience - that's what the original sales pitch for them was: why spend time and effort cooking, when you can just have ready made food. Cooking, however easy it is, is something you have to add to your daily schedule. This isn't much of a problem for those who are adept cooks, for them the time and effort used is really not a problem. But for unseasoned cooks, even the simplest things can seem overwhelming - in my work I've had to teach young adults in their 20's how to hold a knife and cut vegetables because they just couldn't figure out how to make a simple salad. They'd never had to.
These are obstacles that are made worse by our society and living environment. Education and information can only go so far as long as you don't need to implement what you've learned to your daily life. The thing about motivation is that whatever the task it's something that is needed to achieve something that requires extra effort to accomplish. Why is the default setting in our societies unhealthy living?