Food manufacturers do not care if we stay healthy, but they're also not interested in harming us on purpose. Their goal is to maximize profit, which usually means cheapest ingredients with addictive properties produced as quickly as possible by low-cost labor.
But they also know this only works if the market allows it. If nobody bought their snack cakes (random example), they would stop making them. But their snack cakes are designed to make you want to eat the whole package and sold cheaper than an alternative like a healthy fruit and nut mix, making the consumer's choice almost a moot point since consumers tend to trade their own best interests for convenience and "saving" money.
And so, they give the market what it buys. Simple as.
But I do hate it. I have to put a stupid amount of effort into eating healthy because I don't have room for a garden and healthier alternatives are often more expensive. I can see why most people just reach for the snack cakes and call it done.