The reason naturalism can't be pragmatic in its epistemology starts with its metaphysics. Science tells us that we are components of the natural realm, indeed latecomers in the scheme of things that goes back 13.8 billion years. The universe wasn't organized around our needs and abilities, and what works for us is just a set of contingent facts that could have been otherwise. Among the explananda of the sciences is the set of things that work for us. Once we have begun discovering things about the universe that work for us, science sets out to explain why these discoveries do so. It's clear that one explanation for why things work for us that we have to rule out as unilluminating, indeed question begging, is that they work for us because they work for us. If something works for us, enables us to meet our needs and wants, then there has to be an explanation for why it does so, reflecting facts about us and the world that produce the needs and the means to satisfy them.