Sugar is part of it but also crappy boxed/packaged foods filled with chemicals that slow the bodies ability to metabolize. That’s just a guess, I have no data on that but it makes sense.

And lifestyle and inflation. People are more sedentary than they used to be and picking up fast food instead of cooking isn’t a rare thing anymore. When I was a kid we would get take out once a week on Friday night. That was the only non home cooked meal of the week. There are people now that eat take out three times a day.