Maybe…but two things:

If the number of obese people is lower, then what are the people who aren’t mildly overweight? They are healthy weight. So even if the percentage of mildly overweight people stay the same, the day to day comparison is with a bigger group of healthy weight people, so they probably were more recognizably overweight.

Secondly, with less really obese people you wouldn’t get desensitized to seeing fat all the time, which makes mildly overweight people seem more normal. Somebody with a BMI of 26 and about 15lbs overweight would have been more likely to be described as “plump” or “husky” back then. But when crowds are full of people that are 50+ lbs overweight, that 26 BMI seems downright healthy.

This is all speculation. I can’t remember how I perceived overweight vs obese people back in the 80’s.

That’s the thing 40 years ago you would realize that they were overweight.