That's much more easy to say than to do, unfortunately. Even I sometimes violate what I just said. Cheaper stuff is always more appealing. I have no idea how we can ever solve this growing problem.
It is possible to eat healthy for cheap. I believe that is why many people raise chickens and have gardens in the first place.
People buy unhealthy things for two reasons: because it is cheap and fast to prepare. So, if we can make healthy food cheap and fast to prepare, people will eat healthy. Making healthy food cheap is easy once you find a way to make a productive garden. There are ways to make it fast and convenient, too. If you look up "mealprep" you will find how some people like to do it.
Here's a decent example:
This man prepares simple, healthy meals ahead of time so all he has to do is reheat them when he is hungry. The price would come way down if it involved garden produce, and that would also provide more variety. This man eats the same things for lunch all week, that is definitely not how most people do it. Anyway, that is just one example. Some people do an extreme version called OAMC or Once A Month Cooking. A family spends all day cooking, then freezes everything to be reheated later, so they only have to cook once a month. That seems much more hectic than doing mealprep once or twice a week, but I think the point is that buying in bulk saves money.
My point is healthy eating does not have to be expensive or difficult. I hope it gave you something to think about.