There are people who have genuine medical reasons for being overweight and there always have been.
A friend of my mum's was always slim until she had steroids for infertility in the 80s. She became very big while her diet hadn't changed at all.
But these medical reasons don't and won't apply to everyone or even the vast majority. There hasn't been a huge medical crisis in the last 40 years. Its a dietary one. The availability of crap food. A lack of understanding around crap food. And a lot of people.just like the taste of it (no matter how crap it is) and want to eat it.
The way UPFs are designed, they trick your brain.
It's not real food and your body doesn't recognise it as real food, which is why the normal 'full' or 'enough' triggers don't work.
I could eat a whole medium sized dominos pizza by myself in one sitting. And have done. I couldn't eat that amount of food of something I'd made myself from scratch because I'd be full after the equivalent of 2 or 3 slices. If I ate the equivalent of a whole dominos pizza to myself for one of my meals every day, I'd be obese too. And some people do.
And are still hungry because that's how those foods work.
And there's just no getting away from that.
And I say that as someome who has been 'very overweight' although not obese; someone who is related to people who are/have been both obese and slim; and someone who has lived with people who are/have been both obese and slim.
In no case were there any 'medical' reasons for the differences in size. But a huge difference in terms of food choices and quantity of food consumed.