There are multiple reasons for that, but none of them are because it's the best way to lose weight. I used to think it was, and I've been going to the gym religiously for a couple of decades. I was always fit, but never lost the weight I wanted until recently when I discovered that eating less is the best way to lose weight. When I would go to the gym, I would compensate by eating more, which is why I never lost weight.
The high level bit, the primary action is exercise makes you stronger. Not exercising makes you weaker. Eating adds mass, not eating removes mass. It's so simple and symmetric, it just astounds me how long I believed that the primary way to get skinnier was to exercise.
I was afraid to eat less, and extremely resistant to counting calories (and I believe many many people are in the same boat). How many diets advertise being able to eat as much as you want of certain kinds of food and still lose weight? How many gym commericials advertise gyms for weight loss? Most gym ads sell gyms as a way to lose weight, most of society talks about gyms as a way to lose weight, it's no surprise that people think of the gym as a weight loss tool and as a way to avoid counting calories, or worse: being hungry.
The replacement technique in the article is exactly what I had to use to get over the fear of hunger. I had to figure out a way to mentally realize that my hunger meter was mis-calibrated, and that if I didn't feel a little bit hungry, then I was eating too much. I had to re-adjust to realize that not being hungry was a bad thing. This is opposite of feeling like I need willpower to overcome hunger.
> I cannot neglect the fact that after 3-4 months of gym I get in a perfect shape and lose 8 lbs minimum.
You're lucky; your eating is under control and you don't over-compensate when you work out. But many people do if they're not careful, which is why advising gym use for weight loss is usually ineffective (and can even damage some people's will and/or self image). Advising gym for getting stronger is great.