CICO at its mostasic level does work. Ever since homo sapiens first walked the Earth, we've known that if you continue to not ingest enough food, you end up dieing of starvation.
But food isn't just about calories. It's also about vitamins and minerals and so on. 100 calories of broccoli isn't the same as 100 calories of sugar.
I got a referral to the dietician because I have had low iron and low B12 in the past, as well as high cholesterol, high blood pressure and high blood sugar, and often things which are good for one (e.g. red meat good for iron isn't so good for cholesterol, dried apricots good for iron, not so much for blood sugar, etc.) I eat a fairly broad diet, including lots of vegetables, but I think there must be some adjustments I can make, that I can get all the necessary nutrients from the food I eat and also not increase risk factors in health, and I don't want to eat nothing but kale, even though I like it. But all the dietician would talk about was losing weight, and offered to refer me to WW or SW, and didn't answer my actual questions at all. I can lose weight - I am slowly losing weight. But I want to make sure I am getting enough nutrients as well.
And on top of actual nutrition, food feeds other senses. Sometimes, I want something nice and crisp like an apple or celery. But sometimes I want something the soft, springy, chewy texture of bread or a doughnut. Or a creamy texture. Or crunchy. And then there's the smell and flavour.
And the social and ritual aspects of food. I don't think a blow-out once in a while for Christmas and birthdays is bad, but I think we get special meals far more often than a century or more ago, and if it's happening fortnightly or weekly, when it was once once quarterly or something, it does add up.
So I don't think CICO can work unless you also looking at the other aspects of diet. Otherwise, you could lose weight by eating just 1000 calories a day of sliced white bread and nothing else. But you might die of beri beri or scurvy or something instead of obesity issues.