They have no willpower. You are the only person who controls what you eat everyday. If you are in stuck in an office you need to block out time for exercise.

How can there be any other excuse?

I know people who look great and eat entire cakes each day but they do 4 hours of high intensity exercise everyday. I can't do that as I am fundamentally lazy and only exercise/diet for vanity.

IMO you have an oversimplified view of this based on limited experience. You have abstracted away the diverse and complex reasons this doesn't work for everyone behind the excuse that people make excuses. It's not so simple. People are different; their circumstances are different; we can't just write them off by blaming them for being obese or addicted.

A legitimate reason I can think of is that eating healthy food is expensive and people in poverty can't afford the luxury or spare the time.

I have meals prepped and delivered twice a day and a trainer 3 times a week which obviously helps somewhat