Why Is At Attin a Hidden Planet in Star Wars: Skeleton Crew?

Image from ComingSoon.net

• According to the owl-like creature Kh'ymm, At Attin was deliberately kept hidden to protect it from threats, as it's the last surviving 'Jewel of the Old Republic' - a group of wondrous, secretive planets
• There are theories that At Attin may have destroyed the other Jewels to ensure its own safety and hoard their treasures, suggesting the planet is hiding something sinister that could shake up the Skeleton Crew's mission