The utter failures of governments to provide any meaningful guidance, or intentionally boosting certain product consumption.
We can have an argument on how effective that propaganda was, but in the end governments in EU and US make bad food much more available than traditional diets.
We can all rant about how evil corporations are for putting HFCS into their products in the US, but it's disingenuous to disregard the fact that US government spends billions on propping up corn production that makes HFCS more economically viable.
In the end you still choose to buy sugary cereals, but if you are in poverty - you're left without a choice when it comes to calorie sources, because of government interventions.
Maybe watch https://en.wikipedia.org/wiki/The_Corporation_(2003_film) and it's sequel from 2020 (linked from there) for starters?
Like support for dairy industry came before the dairy industry got enough money to lobby... and sustain itself through lobbying.
Same goes with HFCS, and many others.
It's unfair to argue "evil corporations", when these corporations are made evil specifically by the government intervention in the first place.
I can guarantee you, that should US government pull all financial support for the dairy industry and support plant based products - these corporations will move to plant based alternatives. Because their pure interest is to make money the least cumbersome way.