>>8733418My headcanon is that while Primus does create new transformers/sparks via "hot spots" (I wish the comics had come up with a better term), he is asleep and dreaming. There are themes, forms, and personalities in his dreams which ebb, flow, mutate, and combine. He dreams of the past and future of his children, of Earth and Unicron and the Beast Wars.
The ancestors of the Quintessons took advantage of this though they never knew the true nature of Cybertron as the body of Primus. They discovered this world that created its own cyberorganic life and through experimentation found ways to influence what it would create, resulting in the transformers. The people who would transcend flesh to become the mad and cruel Quintessons were humanoid and greatly enjoyed having loyal humanoid servants who doubled as transportation and weapons of conquest. How and when they transitioned into their current forms has been lost to time.