Maybe these people know that diets (by whatever name) don’t work and they are sick to death of hearing about it.
“You can initially lose 5 to 10 percent of your weight on any number of diets, but then the weight comes back. We found that the majority of people regained all the weight, plus more. Sustained weight loss was found only in a small minority of participants, while complete weight regain was found in the majority. Diets do not lead to sustained weight loss or health benefits for the majority of people…In addition, the studies do not provide consistent evidence that dieting results in significant health improvements, regardless of weight change. In sum, there is little support for the notion that diets lead to lasting weight loss or health benefits.” Link to study here
Or this: “We believe the ultimate goal of diets is to improve people’s long-term health, rather than to reduce their weight. Our review of randomized controlled trials of the effects of dieting on health finds very little evidence of success in achieving this goal. If diets do not lead to long-term weight loss or long-term health benetfis, it is difficult to justify encouraging individuals to endure them” Link
“Consider the Women’s Health Initiative, the largest and longest randomized, controlled dietary intervention clinical trial, designed to test the current recommendations. More than 20,000 women maintained a low-fat diet, reportedly reducing their calorie intake by an average of 360 calories per day and significantly increasing their activity. After almost eight years on this diet, there was almost no change in weight from starting point (a loss of 0.1 kg), and average waist circumference, which is a measure of abdominal fat, had increased (0.3 cm)” Link
And, because they know that healthy habits are good for anyone of any size
Or maybe they’re tired of people who are lipophobic
So, factually, it isn’t more detrimental. It’s entirely possible to be fat and fit and healthy, but no one ever wants to hear that.
As for me, I used to subscribe to “eat less, move more,” to lose weight. Unfortunately, bodies are far more complicated than that.
IMHO, if someone wants to lose weight, it is not my business. If they ask for my thoughts, I will direct them to this information with the caveat that this is what I think is right. They have minds of their own and it is not up to me to police their thoughts or beliefs any more than it is up to someone to be my food or exercise police.
After that, what @rory and @CWOTUS said.