> It's that I have a desire to eat dramatically fewer calories on a low-carb diet

Precisely my experience as well. While it’s true that really no one type of nutrient is universally bad or evil and technically weight loss comes down to calories in/out, there is a huge difference in how satisfied you feel after eating X amount of calories in various forms. I can eat an entire loaf of good bread or a big bag of chips without even thinking about it. Fats are tasty too but I don’t find myself wanting to gorge on them to the same extent.