“For example, is the statement “No one can decide for any other being maters of truth” true? If it isn’t, then why consider it?”

I think what has driven Western philosophy, at least, is the desire to arrive at rationally derived rules that (all) people and (all) societies should live by: How should humans be governed? That has necessarily fueled inquiries into epistemology and ontology.

The advent of civilization, as opposed to the homogeneous societies that have existed outside it, engendered a requirement for some rule(s) to govern governance; history tells us that the default ‘value’ is ‘rule by the most ruthless’. The impetus for philosophy’s existence is the attempt to supplant that with a ‘better’ rule, the validity of which no one can deny. According to the “Axial Age” theory, various existing religions as well as the Buddha, Confucius, and the Greeks were all taking up that question in the same period of history.

I am not among the postmodernists, but I accept as valid aspects of their critique of modernity. I think their big error was a failure to distinguish between beliefs (extra-rational assertions, whether secular or religious) and ideas, which are products of the rational capacity. People can reason from beliefs, but all such reasoning is in the service of a belief. Ideas can have beliefs for sources, but to be a a strictly rational idea it must be able to be evaluated without reference to any belief (which would include any a priori assertion of anything). So, like modernists, postmodernists have mistakenly taken ideologies, which are based on secular beliefs, to be exemplars of ‘the rational’. Ideologies are secular versions of theologies.