Geometry, Algebra, and Arithmetic are used to create maps and models of physical phenomena. This is 'objective idealism' or the linking of ideas to objects to create objective relationships. A map is and illustration of a certain phenomena. It doesn't explain why the phenomena exist.

What is a subject's relationship with objective reality? What is a subject's relationship with other subjects? What is a subject's relationship with him/her self? These are the questions metaphysics tries to answer.

Objective idealism of Modernity tried to 'flatten' all reality down into subject-object interactions. This reduces knowledge down into only objective knowledge. What about social knowledge? What about subjective knowledge? These other maps and models of reality are lost for the purely objective.

This fracturing of knowledge makes science good at explaining the pieces and parts, but has no way to put them together into a complete system of knowledge. We see this in complex issues such as climate change. Science can explain what is happening, but they cannot answer the social questions about how to fix it. Instead we leave that up to politicians, because somehow politics is more rational than science!