You almost take on a moral fervor. Your rhetorical question suggests that underactive thyroid function led to your obesity. This is rarely the case. However, thyroid deficiency as a cause of obesity would be a medical curiosity. Hypothyroid patients may be stout and puffy, because they retain fluid.
Overweight people get that way, as a rule, because they consume more calories than they burn.
Incidentally, doctors may make snap diagnoses of obesity because, like high blood pressure, the diagnosis depends solely on the numbers. If you weigh 300 pounds, you're obese. Media doctors try their best to guide patients to additional resources, rather than second-guessing or making impulsive pronouncements. If that doesn't work, seek medical attention. I have a constant sweet taste in my mouth, as well as headaches and lightheadedness.