Why most people do not care about nutrition?

Some do!: Some people do care about nutrition. They educate themselves & feed their bodies for long-term health. Others feel that if results aren't immediate, why bother? Habits with food, alcohol, drugs, and exercise require commitment to change. Dietary interventions often take at least 3-6 months to show effects in how you feel, so for a time you're operating on faith. Many say it's worth it, though.

Education: perhaps they have not been educated about the benefits and advantages of nutrition. In my medical school, nutrition was not a big part of my training. I actually went ahead and did two years of specialized training in nutrition. I think awareness and education are the best ways to get people to know and care more about education.

That's life.: Unfortunately, caring about your health is effortful and expensive. It's easy and cheap to eat poorly and not exercise.