Except that they don’t. To repeat, there isn’t one verse in the Bible that explicitly or directly states God is an absolute unity (one person; unitarian).Unitarians follow sola scriptura.
That is not what it says:According to your peoples' Athanasian Creed the god is the substance or essence divided among the members of the trinity.
1. Whosoever will be saved, before all things it is necessary that he hold the catholic faith;
2. Which faith except every one do keep whole and undefiled, without doubt he shall perish everlastingly.
3. And the catholic faith is this: That we worship one God in Trinity, and Trinity in Unity;
4. Neither confounding the persons nor dividing the substance.
https://ccel.org/creeds/athanasian.creed.html
Creeds are summations of what the Bible teaches. And the doctrine of the Trinity best takes into account all that the Bible reveals about the nature of God.When we speak of the trinity doctrine we should be careful to define what it is we are talking about. It's not something in the Bible. It has to be supported by a creed.