I don't know you or where you are coming from, but it seems like you want people to take personal responsibility.

That's fine. People do need to take personal responsibility.

The answer can be more than that.

When I was younger, I wondered how any smart person could ever be obese. It did not make sense to me how someone could not figure out how to solve this problem. It did not seem at all complicated to me. Through my 20s and mid 30s, I was able to maintain a healthy weight, but increasing over time.

There are two different problems here that get lumped together: Why do people gain weight, and Why is it so hard for people to lose weight even after it's obvious that they should.

Maybe you want the world to be simple. That's fine. That's normal. It's hard to understand a complicated world.

Everyone understands that their own life is complicated, their own job is complicated, their own problems are complicated. Maybe other people also have complicated problems. Maybe.