You seem to be dodging the obvious: the "why" is because a company has no value when you are risk-free and comfortable because it gets nothing from the inputs towards you, only from your outputs. That doesn't mean it is exactly that black-and-white; your input and output are related. Then there is the availability thing; people with skills and experience are not easy to find so you often want to retain them at the company, and compensation is a great motivator.