I would expect that comes down to finding something you enjoy doing.
Exercise and eating well is a way of life. If your life dictates you do neither, you will get fat. I don't really understand how its complicated. You just do it for the benefits.
Personally I eat chicken and veg 5 days a week (with occasional carbs when I train), train for 3 days and climb once a week. I also mostly hit my 10k steps per day.
If there's an obvious solution that so many people are having trouble implementing, what is more likely?
1. That all those people are stupid or have no willpower, or 2. that the obvious solution doesn't work for everyone?