The problem with a high carb diet is that you are triggering consistent high levels of insulin--this causes glucose to be stored as fat. Additionally, the high insulin spikes causes your blood sugar to get low and then you are hungry again, making you more likely to eat more and have additional calories. And this is why so many people end up consuming more calories than they burn leading to weight gain
High protean/high fat and low carb diet doesn't cause the above problems, which is a large reason why it is easier to lose weight on that diet. Additionally, our body uses protein and fat for so many things, whereas we only use carbs for energy and nothing else. When not used for energy, carbs are stored as fat