What separates a high roller from a major
Field size and quality. A major has thousands of entries with a wide skill spread; a high roller has dozens, most of them professionals who play these events full time. The same strategy that crushes a Sunday major is close to break-even against that group.
Structures are also deeper and slower, which increases the number of decisions per event. Deeper play magnifies skill differences — which is excellent when you are the strongest at the table and expensive when you are not.