Physics is simple, because it studies reality at the fundamental level. New ideas in philosophy / religion / politics / art rarely change how physical systems w

Physics is simple, because it studies reality at the fundamental level. New ideas in philosophy / religion / politics / art rarely change how physical systems work. Because physics is so self-contained, you can become good at it by studying primarily physics. Economics is complex, because it depends on every other human activity. You can't become good at economics by studying it. You also have to study everything else.