The most fundamental explanation lies in understanding what the Mahabharata is and what it is not. The Mahabharata belongs to the genre of itihasa — literally, "thus it was," a historical narrative. Along with the Ramayana, the itihasas are records of events that are understood to have occurred in the world of human affairs, involving real kingdoms, real battles, and real moral dilemmas. The Mahabharata's primary concern is dharma — righteous duty, cosmic order, and the ethical complexities of human life. Its narrative revolves around the conflict between the Pandavas and the Kauravas, the question of rightful sovereignty, and the catastrophic war that reshapes civilization.
Krishna's role in the Mahabharata is that of a statesman, diplomat, charioteer, and divine guide. He is the king of Dwaraka, the ally of the Pandavas, the cousin of both warring clans, and the voice of transcendent wisdom in the Bhagavad Gita. This is Krishna as Dwarakadhish — the Lord of Dwaraka, the sovereign, the counselor. This is not Krishna as the playful cowherd of Vrindavan, the butter-thief, the enchanter who dances with the Gopis. The Mahabharata operates in the register of political dharma and cosmic duty, not the intimate register of divine love (prema).
Radha belongs entirely to the world of prema — to the intimate, playful, ecstatic dimension of Krishna's being that unfolds in Vrindavan, not on the battlefield of Kurukshetra. Her absence from the Mahabharata is not an omission; it is a reflection of the epic's purpose. The Mahabharata tells the story of dharma; Radha's story is the story of love beyond dharma.
This distinction is crucial. The Krishna who speaks the Bhagavad Gita is articulating the path of duty, knowledge, and devotion in the context of a world crisis. The Krishna who plays the flute in Vrindavan is revealing a different dimension of the divine — one that is accessible not through duty but through selfless love. These are not two different Krishnas; they are two aspects of the same infinite being, but they are expressed in different literary traditions designed for different purposes.