what makes you think He didn't write it for us?
The fact that throughout it uses the concepts current at the time it was written.
This isn't to say there are not timeless truths in scripture which (to use the words of scripture itself) make it profitable and useful to all generations. But no, it was not written for us. Isn't that a rather arrogant assumption?
Do your concordance search on "spirit". Ancient Hebrews knew the difference between spiritual qualities and physical life.
The Israelites also understood nationhood and characteristics of groups of people. It was again completely unnecessary to make Adam emblematic of all man and of the nature of the fall itself. If Adam represented a stage in evolution, it would be stage shared by a nation.
Joseph also showed comprehension of symbology in his dream of the sheaves of wheat and cows coming out of the Nile. Both symbols were readily translateable adn explainable. The figure of Adam is nothing but trouble for the idea that he simply represents a stage in evolution.
I would use something clearly intended to be a symbol of man if evolution were true.
Obviously the idea of a regional flood would be simple to describe as well. I would just say it that way.
I don't think the comprehension of the ancients is limited by their intelligence or sensitivity in matters of the spirit. In many matters, both mundane and spiritual, the sophistication and subtlety of their thought is very profound and we have in no way surpassed them.
Nevertheless, it is simple fact that some information was not available to them. Some information requires advances in technology before it can be known. So all we have learned in astronomy (dependent on the telescope) and in micro-biology (dependent on the microscope) and all we are learning through space probes, and all that has been learned through the exploration of areas of the earth and civilizations unknown to the ancient Near East and Mediterranean civilizations was simply not available to the authors of scripture.
I think the question is whether any of this additional information, including geological, paleontological and biological information that only became available within the last three centuries, has any major implications for God's relationship to humanity or our relationship to creation and to each other.
There is a huge amount of scientific information that we have acquired since the Enlightenment, but in a real sense it is all spiritually peripheral. None of it, for example, makes the Ten Commandments or the Golden Rule outmoded ethical standards. None of it invalidates scriptural teaching on God's power and glory, mercy and justice. The concern of Isaiah and Amos for justice for the poor, the Sermon on the Mount and Paul's paean to love are all just as valid today as when they were first written.
It seems to me that asking for the spiritually peripheral information science has given us to be part of the scriptures is asking for the chief and urgent message to be delayed until everyone has caught up with the tutorials on modern science.
The lack of modern science in scripture has nothing to do with lack of intelligence or theological sophistication on the part of the ancients. It has to do with spiritual priorities and the necessity of setting out God's judgment of sin and expectations of righteousness without having to wait for the technology necessary to the acquistion of modern scientific knowledge.
Consider the analogy of a missionary doctor taking medicine to a remote Papuan tribe that believes all illness is caused by demons. In the midst of an influenza outbreak, does the doctor take time to explain germ theory before administering inoculations, or does he say he has brought them a new way to combat the demon that causes the flu? If the need of immunization is urgent, would the doctor not explain it in terms the tribe understands and get on with education on the causes and transmission of disease when the urgency has passed?