and the question is why more people do not do the same

I find the whole idea of diets, as normally presented, weird. There is a cultural, ethnic and family tradition of what meals to cook and eat for me. This is part of my identity and lifestyle. The first issue is that diets do not even talk about meals, they talk about ingredients: meat, vegetables etc. are ingredients, a peas and chicken breast casserole in so-and-so sauce is a meal. So unless diets are meant for people who were always, no offense, eating boring as a family tradition, in a meat-and-two-vegs style, diets are weird. I am not eating meat or potatoes, they are merely the ingredients of the meals.

The same way you don't eat "flour" or "wheat" or "grains" or "carbs", you eat e.g. Italian sourdough bread from so-and-so bakery, so diets that talk about flour/wheat/grains/carbs get the inferential distance, the mental map completely wrong. They require a huge cognitive effort and facing unfamiliar and non-obvious thinking.

I mean, the point is here that diets want you to think bottom-up, you want to eat X ingredients and look for recipes for them. This is a huge distance from the usual, normal thinking, which is top-down, that you eat meal Y and buy whatever ingredients the recipe requires or buy the meal ready in a restaurant or somewhere and don't even know the ingredients. (I can identify the cucumbers in my restaurant ordered Stroganoff but not sure if the other tidbit is mushrooms or what, example.)

Add to it the factor of finding out the ingredients in everything you did not cook yourself, from your aunt's cake to the street hot dog (brown-bagging every work lunch is another "boring guy" territory to me, it is just too "anal" to not eat random things that are offered but carry your food supply the same way an astronaut carries oxygen supply).

Instead of all this weirdness, I manage my weight with 1) cutting down on vices, snacks, sugar soda (just drink coke zero) etc. stopped boozing etc. 2) intermittent fasting, as not-eating is never cognitively weird and probably autophagy is one of the most important parts of dietary health (read Eat Stop Eat). This is not an easy process either, I think I got to the point where the calories are right, so now the potential issue is micro-or macronutrient deficiencies.

My larger point is that any specific diet is merely an instance of the more generic class of being on diets, on being choosing and conscious about eating instead of drifting in a largely unconscious family and ethnic tradition, and I find that cognitively difficult and weird. However, it is a classic case of being the average of the five people you spend the most time with. If diets in general are normal in your subculture or culture, it is easy to adopt one, so basically your friends going pale can help you go vegan because they both are subsets of the whole choosy and conscious eating thing. If diets sound like some weird new sissy fashion to most people you spend time with and they make fun of "reform kitchen" and everybody just drifts in their ethnic and family tradition or whatever can be bought on the street, you will also find it hard.

(I should also say I am not longevity oriented because I find it hard to fill out time with goals. But the quality of the 60-65 years I roughly expect to spend alive does matter, hence the experiment with things like intermittent fasting.)