Because sport functions in a much different manner than most occupations. It is driven significantly by adrenaline and aggression. In a typical office setting, aggression is generally counterproductive. If a boss yells at people, it is likely to engender resentment rather than motivation, because the work being done is usually not made any more efficient by aggression or adrenaline. Reasoning, logic, calculation and efficiency are far more important. Writing a report, calculating finances, managing shipments or whatever else are fundamentally different than playing sports, because they utilize different cognitive processes.
In sport (generally, something like pool, darts or golf is less applicable), physical capability, instinct and determination are primary mental processes. Even an intelligent player not noted for his running, say Xavi, is still not thinking in the same sense that an account manager at work is thinking. Entirely different areas of the brain are being used. The thinking is faster, more primal, and in most cases subconscious. In a physical struggle such as either American or association football, hockey, basketball etc, calm reasoning (such as would be appropriate for an office) loses efficacy because it doesn't speak to the mental processes being used on the field (pitch, ice, whatever). A more primal form of communication is required at times.