Simple, if any religion was true and objectively based in reality, why the fuck do they need missionaries to spread it?
If any religion was true, it would have measurable, verifiable, and predictable traits that would be discovered in isolated societies. If all of mankind’s knowledge was erased, we would eventually rebuild our understandings of physics, biology, chemistry and mathematics as they are today. If all knowledge of religions were erased, we would never get the same religions back.