Healthy food is more expensive both in time required for prep and materials. That is why affluent people seemingly buy healthier food. When you grow up poor, or live poor you don't have as much time or mental energy to properly diet.
Indeed. Despite my snobbery, I appreciate that it's not a purely moral issue. And I suspect that an effect of mental energy is being able to withstand marketing and cultural forces, peer pressure, etc.
Often poor means underemployed, not overworked. It's the middle class that have no time.