That example is pretty much my history.
In highschool I topped out at about 285. At 6'1"-ish and stocky I was about 35-40% bodyfat. When I got down to about 180 at my thinnest, I was working out twice a day, living off of smoothies, sugar free tea, and meal replacement bars. The moment I began reintroducing normal foods (not junk, just recommended daily value sort of stuff) I started gaining back weight. I started going to the gym only 3-4 days a week and I started gaining it back quicker. Compared to my friends I was eating far less, and working out far more, and I was gaining weight. Diet and exercise DOES work, but I was not particularly interested in maintaining a lifestyle that meant denying myself all of my favorite food and spending 10-15 hours a week in the gym. I settled into a weight around 230-240 a few years ago and it appears that is where I will stay unless I pick up that gymrat life again.
Well its a lifestyle choice (as I said) your lifestyle doesnt include working at being a normal weight. Not a criticism, but almost anyone who says they cant do it decide not to...btw that includes people with thyroid problems...ive known people to overcome that with exercise and radical changes in diet.
BTW I can eat 6 meals with healthier food (not smoothies)and easily lose weight. It requires some discipline but doesnt necessarily mean changing everything about your life.