Using this stolen power, Yaldabaoth creates a material world in imitation of the divine Pleroma. To complete this task, he spawns a group of entities known collectively as Archons, 'petty rulers' and craftsmen of the physical world. Like him, they are commonly depicted as theriomorphic, having the heads of animals. Some texts explicitly identify the Archons with the fallen angels described in the Enoch tradition in Judaic apocrypha. At this point the events of the Sethian narrative begin to cohere with the events of Genesis, with the demiurge and his archontic cohorts fulfilling the role of the creator. As in Genesis, the demiurge declares himself to be the only god, and that none exist superior to him; however, the audience's knowledge of what has gone before casts this statement, and the nature of the creator itself, in a radically different light.
The demiurge creates Adam, during the process unwittingly transferring the portion of power stolen from Sophia into the first physical human body. He then creates Eve from Adam's rib, in an attempt to isolate and regain the power he has lost. By way of this he attempts to rape Eve who now contains Sophia's divine power; several texts depict him as failing when Sophia's spirit transplants itself into the Tree of Knowledge; thereafter, the pair are 'tempted' by the serpent, and eat of the forbidden fruit, thereby once more regaining the power that the demiurge had stolen.
As is evident, the addition of the prologue radically alters the significance of events in Eden; rather than emphasizing a fall of human weakness in breaking God's command, Sethians (and their inheritors) emphasize a crisis of the Divine Fullness as it encounters the ignorance of matter, as depicted in stories about Sophia. Adam and Eve's removal from the Archon's paradise is seen as a step towards freedom from the Archons, and the serpent in the Garden of Eden in some cases becomes a heroic, salvific figure rather than an adversary of humanity or a 'proto-Satan'. Eating the fruit of Knowledge is the first act of human salvation from cruel, oppressive powers.
So it seems to me that the early churches took the story of the Demiurge and made it their own. Turning him into Satan. Probably just to scare people and make them obey.