Because they fail to address the hormonal root causes that are the most common reasons for weight loss resistance, like excess cortisol, insulin and/or leptin blockage, oestrogen dominance, a sluggish thyroid, low testosterone, and problems with the HPA (hypothalamic–pituitary–adrenal) control system.
99% of the time, the main hormone that's out of whack is cortisol
(which ends up disrupting other hormones, too). Your body makes cortisol in response to stress, but most of us run around stressed too much of the time, and our cortisol is off as a result. High or dysregulated cortisol levels wreak havoc over time, depleting your happy brain chemicals like serotonin, robbing your sleep, and making you store fat—especially in your belly. High cortisol is likewise linked to depression, food addiction, and sugar cravings.
The root cause of cortisol imbalance is usually a dysregulated HPA (hypothalamic-pituitary-adrenal) axis, which is the boss of all of your hormones. When the HPA is up-regulated, your body produces too much cortisol and the results are: muffin top, feeling like you're constantly racing from task to task, feeling wired but tired, quickness to anger and irritability, rapid weight gain.
Over time, the HPA can get burned out and become down-regulated. Then you feel a lack of stamina, have a tendency to hold a negative point of view, catch colds frequently, and you may experience thyroid problems that improve briefly before you crash again.
Since the root cause is usually the HPA, the key is to reset it, starting with cortisol. Any other attempts at fixing the hormones will likely fail in the long-term if the wayward HPA is not addressed.