One part of an answer to the "western culture" question above is that symptoms have an immediacy that the underlying illnesses do not. It is unacceptable to let fat children die in car accidents while attempting some sort of health education reform for the nation. Therefore, larger seats must be made.
Human beings have the gifts of foresight and hindsight to a degree, but we don't always apply them rationally. In a way, we apply them too rationally. As an example, if any given day I choose to eat a 1200 calorie donut, rationally, there is going to be little disadvantage to me. One donut, even a calorically massive one, is really not going to change my level of health in any lasting way. On the other hand, it will provide immediate pleasure. It is only when looking at a pattern of behavior, or looking at the long term consequences of continued indulgence, that it becomes clear that I must regulate my behavior.
Of course, true rationality would require that we use our reason in accordance with the nature of the thing, and we ought to know that single behaviors become habits, which imply long-term effects.
Further, to heal diseases and not symptoms, we must have an idea of what the disease might be and what we might do to treat it; we must also know what constitutes a cure. If a disease is hidden from us (asymptomatic), it will take quite a long time before we are able to identify it and treat it. We rely on being able to identify something as the proximate cause of something else; it is very difficult for science to advance when one cannot establish causation or at least correlation.