The main reason I know of why it would make sense to write it that way is that’s what everyone believed at the time, and if you told them otherwise, it would seem implausible to them. Thus, we must keep in mind that some phraseology has a specifically ancient audience in mind.
Before I go any further, I should specify that I am a paleontologist who has studied other areas of science, and am not an expert on the ancient near east.
My thoughts on how the world was created are basically the following:
Sometime around 13.8 billion years ago, God did something to cause a large amount of mass in a singularity to rapidly expand, followed by exponential expansion, as it did so, it cooled and formed particles, likely with some sort of guidance to create a matter-antimatter imbalance. Skipping forward to about 5 billion years ago, God guided a series of collapses within a gas cloud in the galaxy we now live in, and from those, stars with proplanetary disks formed. Within one of those, as planetesimals formed, God caused the formation of a dozen or so large bodies, perhaps five or six were cool enough to accumulate gas, and become gas giants. Smaller bodies then accumulated closer to the star. The gas giants then migrated outward, causing many smaller bodies to begin drifting inward. Two of the larger bodies formed on the same orbit, within the habitable zone, on lagrangian points of each other, God then caused perturbations in the orbit of the smaller body, resulting in it crashing into the larger body at a somewhat oblique angle. This formed a debris disk, which the coalesced into a very large moon. This large moon would keep the planet’s axial tilt much more stable, and thus make it more suitable for life. Within the liquid water that began to accumulate on the surface of this planet God caused the exact set of molecules needed to form simple cells to form and come together.
As to interpreting the earliest chapters of Genesis, I would consider the time span of seven days to be symbolic of completion, and the main point to be “God made everything, so no creature in the sea is going to challenge him, the way they do in the beliefs of all the other cultures around you.”
As to creation of humans, my thought (this is speculative) is that God guided evolution the produce members of the subspecies Homo sapiens sapiens about 300,000 years ago in east Africa, then directly created Adam and Eve in what is now the Persian Gulf something like (very roughly) 100,000 years ago. My speculation is that Adam and Eve were the first humans to have a soul, to have a complicated language, and other uniquely human traits which are not observed elsewhere. As to original sin, I would recommend reading the opening post in the discussion of A. Suarez’s Treatment of a Pope’s Formulation for Original Sin Transmission.
Again, these are my thoughts, not a definitive answer.