The real answer is more a question of RPG tradition. Pathfinder and Golarion follow directly in the footsteps of D&D (via DD3.5), a gaming tradition going back to the early 70s.
D&D-esque RPGs have long borrowed from Earth religions and mythology. Already, in '76, we had Gods, Demigods & Heroes from TSR, giving game statistics for gods and other deific beings from a wide range of earth mythologies, as well as a few from fantasy literature.
Some RPGs were specifically set in a fantasy version of Medieval Europe, like Chivalry and Sorcery, and used real-world religions. But the overall tradition was to use made up religions and gods, only occasionally borrowing directly from real-world mythology, like the Osirion pantheon of Egyptian-inspired gods. MaskedGuy's answer is the in-game link, but IMHO it goes further than that.