Your comment implies that the "employers" recognize persons doing very valuable work for the organization who are irreplaceable. That is not true. Most employers have no feelings for the prosperity of the organization, except in proprietorships. The worth of an employee is recognized, if at all, only after he or she has left.
Actually, until you decide to leave to go somewhere they will pay you what you are worth, your manager will never accept that you are a top performer. "Facts are stubborn, but statistics are more pliable."