This is a question for all you who believe in Scripture.
Scripture is defined as "sacred writings." Sacred is defined as "connected with God".
It is believed that God or gods spoke to individuals and they then wrote down what was heard.
I understand why people thought to write what was heard down.
What do you think was the purpose of God to speak to them?
Your question pertains to complex issues.
Without sin having entered the world, God would only have needed to talk to us to instruct us how to live morally and later how to establish rules for our technology that would avoid our destroying the earth.
With sin entering mankind in general, the issue of the ransom, redemption, the restoration of mankind to perfection by those means and God's theocracy became necessary subjects. At the same time, the march of the nations was given to let us know the ballpark of when things would be restored. The problem of satan ruling the world surely has impacted all, and also believers. These issues have needed much teaching by God.
If you look at animals, only mankind has the divine like ability to change their world with technology and destroy the world by their actions. Because we are god-like, we have needed his instruction though we have a lot of instinctive things working within our bodies and through our societies by extension. Animals can live entirely by instinct; we cannot. To let those of us who listen to His Word be assisted by the word and by His angels, He has given us His inspired writings to deal with a global society ruled by the demons and their ruler satan. In this way, we can by faith live and die according to His purpose until it is time for the restoration fully knowing what God shall do for us.
The reason God spoke to singled out individuals, prophets, was to avoid having to speak to everyone all the time. While we can speak to God in prayer; He speaks to us via his inspired word and His spirit (for those who can listen to it and have the means to listen, the robes of righteousness).