I think you are confusing theology with one of its sub components: doctrine/dogma. A systematised description of theology is only one approach to theology. In fact your comment (below the question) that the Christian New Testament does contain theology in the letters shows that your understanding of theology isn't broad enough: for Christians the Gospels are fundamental for Christian theology, equally important as the letters, because theology is about knowing God. Theology is so much more than just knowing about God in an informational sense.
Exodus 6:6-7: Say, therefore, to the Israelite people: I am the Lord. I will free you from the labors of the Egyptians and deliver you from their bondage. I will redeem you with an outstretched arm and through extraordinary chastisements. And I will take you to be My people, and I will be your God. And you shall know that I, the Lord, am your God who freed you from the labors of the Egyptians.
Deuteronomy 7:9-10: Know, therefore, that only the Lord your God is God, the steadfast God who keeps His covenant faithfully to the thousandth generation of those who love Him and keep His commandments, but who instantly requites with destruction those who reject Him—never slow with those who reject Him, but requiting them instantly.
My son, if you accept my words
And treasure up my commandments;
If you make your ear attentive to wisdom
And your mind open to discernment;
If you call to understanding
And cry aloud to discernment,
If you seek it as you do silver
And search for it as for treasures,
Then you will understand the fear of the Lord
And attain knowledge of God.
In the Tanakh we meet a God who created the world and decreed it "very good".
We meet a God who wanted our trust even though he knew that we would struggle to trust him, so he gave Abraham not just a promise that he would do good to him, but a promise, an oath, a covenant, and a sign, when his simple word should've been enough.
We meet a God who deemed to take away the Ostrich's wisdom so that it would crush its own eggs (Job 39:11-18).
We meet a God who was grieved when Israel whored itself to other gods (Ezekiel 16).
We meet a God who loved David and called him a man after his own heart, even though David committed adultery and then schemed to have the woman's husband killed.
And we meet a God who willingly inspired both the beauty of the Psalms and the crudity of Ezekiel 23:20, and calls them both his word.
The Bible is a work of theology, but it takes effort to read and understand, because the goal of the Bible is not to list some facts, but to introduce us to God himself!