>>19124729Because Red already canonically existed. Leaf only existed as a confusingly named non-canon manga character and some concept art before FR/LG. Because the PokeSpe translator groups couldn't pull their collective heads out of their collective asses, and because the first games released in America were Red and Blue rather than Red and Green, everyone is confused as to why the sexy ten-year-old in the slinky dress would be Blue instead of the Blue they know as Blue. Everyone already fucking knows who Red is.
Hence, Leaf.