People fail to lose weight because dieting is HARD.
We live in an age of unprecedented energy availability coupled with low levels of daily activity. People suck at estimating their energy intake, especially when faced with a constant barrage of high palatable and calorie-dense foods. Also, exercise while great for health and strength is a poor weight loss intervention.
The biggest loser study is hardly a demonstration of the inefficiency of CICO either, it perfectly proves it. Restrict someone's intake aggressively, forcefully exercise them and they all lost weight, the issue was weight maintenance post-trial, the intervention didn't address their (largely) psychological issues around food. It's a modern day example of the Minnesota semi-starvation study.
And CICO is not a mantra, it's the law of thermodynamics. Whether you eat low fat, low carb, keto, fast or any other dietary philosophy ultimately they all work by creating an imbalance between energy being consumed and energy being expended. Hormones like insulin are important sure, but it's not the only hormone (I realise this is a diabetes forum) involved in weight loss or gain, or responsible for the issues we have today.
Where I'm coming from? Being diabetic doesn't mean you cannot lose weight or in fact need any special approach to be able to. In fact, one of the very first diets for the treatment of overweight diabetics was Kempner's "Rice Diet" that had patients eat high amounts of rice, fruits and vegetables.
So no, it isn't about balancing hormones to lose weight.