It is of course true that caloric input is a thermodynamic limit and restricting it sufficiently relative to caloric expenditure will cause you to lose weight. (Lisa, in this household we obey the laws of thermodynamics...)

However, not all calories are the same, metabolism is dynamic, and the brain is complex and exerts a powerful influence over behavior.

Increasing exercise will make you hungrier and most people are simply unable to resist this and end up not losing weight. It is why there is a common saying that "you cannot outrun your fork." Restricting calories generally is difficult in today's environment with plentiful calorie dense food everywhere. People don't cook as much as they used to and restaurant meals have more calories than ever.

AFAIK GLP-1 drugs work because they calm the minds desire to eat which is baked in deeply from millions of years of our ancestors struggling to get sufficient food.