I think its because Stargate tried to fit in with existing mythology. Mysterious Crystal Skulls, no one knows about. A council of 13 "gods" in a circle could be anything. What 13? Is that a significant thing somewhere? Stargate (the series at least) had several aliens admittedly pretending to be gods still going by the names we gave them. We have no explanation (that I can remember) of the Indy4 aliens, whose gods they were supposed to represent, how much technology and wonders of the worlds they are responsible for, why we would represent any of them as looking human.

Everyone knows the Ark and the Grail. No one knows about Crystal Skulls, or a lost tribe they made up to fit their own mythology. Instead of going with something everyone knows, they started with something real and added their own fake backstory instead of using REAL backstory and explaining it using aliens.