I understand what you’re getting at. We often want our interpretation of Scripture to make sense within a larger theological framework. Just pointing to the text and saying “that’s just what the Bible says, period!” is not always satisfying for everyone.
Some possible suggestions for why DNC could be important (based on what I’ve read over the years, and also my own speculation). Note that these reasons don’t necessarily assume any single GAE model, and might even assume different ones:
- To establish a discontinuity between humans and the rest of the living world, signifying our uniqueness of being image-bearers of God.
- Similar to 1), but DNC could be the way that God establishes a more personal relationship with Adam and Eve from the very beginning. “Indeed, while Adam is related to the rest of creation, specified by the fact that his body is made of the dust of the earth, his special relation with God is highlighted by the fact that his body is animated by the very ‘breath of life’ (Gen. 2:7)” (Longman, How to Read Genesis, p. 106). The answer can also slightly change depending on what view you take regarding the content of the image of God.
- To establish a more definite act of “ensoulment”. Many Christians have a Cartesian dualist picture of the soul where God can just take an existing hominid body and infuse it with a human soul - hence “refurbishment” instead of DNC. However, other views of the human soul which posit some less separability between body and soul (such as hylomorphic, or monist/physicalist) might make it impossible or awkward for this to happen in this way.*
- The DNC of Eve from Adam’s rib may serve to highlight her suitability as an equal helper for Adam (see Longman, same page). Perhaps if her physical body was merely taken from the existing hominid population, that would bring with it undesirable philosophical/theological baggage with it.
- This is more speculative: Remember that Christ, the Second Adam, came into the world conceived by the Holy Spirit - a special act of creation different from regular conception. Perhaps it would be more fitting if the First Adam also came into the world by a special act of creation?
- (EDIT: as Josh suggests below) DNC could be important to establish an “original righteousness” to humanity which could not be possible if they were generated from regular matter via natural processes alone. This is also linked to a certain view of the Imago Dei.
*Regarding 3), I’m not suggesting, though, that ensoulment means implanting some sort of new genetic material in Adam and Eve, because as Josh has repeatedly said, this would require ongoing miracles and/or undetected scientific mechanisms in order to guarantee that said genetic material would propagate to all of A&E’s descendants, assuming they interbred with other humans. Rather, there could be some complex metaphysical/spiritual machinery going on when ensoulment happens that necessitates God doing it via DNC instead of refurbishment.
None of these theological reasons, at face value, seem to be as important as the reasons for a historical Adam and Eve (no matter if they were DNC or refurbished), but they could be a starting point.