Why does Brahma not take incarnation like Lord Vishnu and Lord Shiva?

Why does Brahma not take incarnation like Lord Vishnu and Lord Shiva? Vishnu is the one and only Hindu God who can incarnate. No other Hindu God can. Why is it so? What is incarnation? Among the incarnations of Brahman, Vishnu is the one and only manifestation, who symbolizes the whole of Atman. Vishnu is the Preserver God, whose Atman has lower and upper limits. Vishnu thus keeps our life between a lower and an upper limit. However, the Preserver function in our life is lost often. Then Vishnu incarnates in us and restores the Preserver function. When Vishnu incarnates to restore the Preserver function our life remains unaffected. Incarnations are different from forms. Shiva has many forms. They are not incarnations. Somnath, Pashupatinath, Nataraj, etc. are forms of Shiva and not incarnations. The different forms of Shakti are not incarnations. Incarnation is a desirable feature. Therefore, this feature is added to all gods, goddesses, and to birds, animals and plants. The fact is that Vishnu is the one and only Hindu God who can reincarnate.