"Health" and "wellness" and "obesity" are all 3 completely different things. You can lose weight in healthy and unhealthy ways. You can gain weight in healthy and unhealthy ways.
Without getting into fad diets' actual biological effects(keto, atkins, whatever the flavor of the week "high fat/protien low carb" diet is) people who are on diets are paying more attention to how they eat than people who aren't on a diet. There's so many confounding factors, plus just people saying "I feel like i'm healthier!" just because they're on a diet. It's a mix of "doing better things than you were doing", your body adapting to a new mix of macros, and placebo affect more often than not.
I run about 80KM a week, I used to have a very well balanced diet with carb loading before long runs.
I first tried a carnivore diet as a joke to tease a friend that was going vegan because of his then new boyfriend and while I’ve seen good results I had blood sugar spikes because of the high protien intake and my lean body mass flactuated quite a bit.
I’ve then tried Keto and for me it worked, my performance and overall endurance improved my blood sugar is now constantly in the range of 4.3-4.7 mol with the lower being just after excercise which is honestly very good for me considering that while eating carbs it did jump to above 7 after a carb loading meal.
Lean body mass has also increased considerably I’ve dropped from 21% body fat to 13% over a period of 14 months while maintaining the same level of activity as I have had for the past decade.
Again n=1 but I’ve seen enough anecdotal evidence and more importantly actual research to think that there is something there.
And that is the whole point it isn’t that simple and there needs to be much more research into this hopefully without commercial interests butting in.
Here's my specific points
1- In many parts of the developed world where food scarcity has been minimized/eliminated, we see increased rates of obesity across all demographics. This is a messy knot of factors that covers everything from social behaviors to availability of nutritious food to education and wealth. If you're going to tackle "why are people so much more likely to be obese than before?" you have a TON of factors to attempt to control for in the decision making. 2- If you're not trying to figure out why people are making their choices, and looking at it from a strictly "how does the body work and is that contributing" the simple answer is: your body more readily converts various carbs into body fat than any other macros (Protein, Lipids, Alcohol), people eat a lot of carbs, and finally most people tend to overeat if presented with more food than they actually need. This is the basic scientific consensus, and explains why your experience with a keto diet was positive. The issue is, as you said, that people are interested in selling meal packages and books and lifestyles and generally getting rich off other people's body image issues/health problems. Carbs play a part of in the obesity spike in recent years, but WHY people eat the way they do is what we need to figure out if we want to solve things.
We also need to understand if there are reasons for far occumulation other than simply excess calories. Fat is an organ it is connected to the nervous system and it stores a lot of crap in it, now does your body accumulate fat to protect it self from junk you eat I’m not sure it’s that simple but obesity is a real problem and we need to find a solution for it which is more nuanced than eat less and excercise because at least to me it seems like a far more complicated issue.