Hopefully sometime soon I will have a chance to connect the dots that lead me to this conclusion. In the meantime, I'll just say that a good metaphor for the global economy is an ecosystem. In an ecosystem, there are causes and effects, but they don't proceed mechanically like a Newtonian system of billiard balls bouncing off one another. Carbon and nitrogen go through cycles that change in unpredictable ways as sunlight and coal-fired power plants and butterflies flapping their wings all trip millions of tiny connections that feedback on themselves. Ecology is a part of biology which is all founded on Darwin. Natural selection is a force as real as gravity. But understanding it is not going to involve a set of equations like f=ma.
So why do economists think about the economy with equations like f=ma?
Ironically, because of natural selection. It turns out that a false belief in promiscuous teleology is the default setting of our view of the world. This manifests itself in school children as a natural tendency to believe in intelligent design rather than evolution.
In economists, promiscuous teleology manifests as a belief in such nonsense as "the purpose of markets" and "natural rate of interest" and "the theory of the firm" and "the labor theory of value."
It's just like why humans don't have fur: because God gave us the brains to make clothes.