Because we can

“… An enormous, and largely speculative, literature attempts to interpret anything important that our brains do today as direct adaptations to the environments that shaped our earlier evolution. Thus, for example, religion may be a modern reflection of behaviors that evolved to cement group cohesion among savanna hunters. But religion might as well record our human response to that most terrifying fact that a large brain allowed us to learn (for no directly adaptive reason)- the inevitability of our personal mortality. I suspect that most of our current cognitive life uses the nonadaptive sequelae of a large brain as exaptions, and does not record the direct reasons why natural selection originally fashioned our large brain.”
Stephen Jay Gould, “The Richness of Life: The Essential Stephen Jay Gould (Hardcover)”, Jonathan Cape, 2006, pp232-233