The Giant Beast World, due to enemy invasions, directly locked itself just like the Tangled Undead World did. It prevented its creatures from advancing to the eighth tier, and also blocked external eighth-tier creatures from entering.
Under normal circumstances, this choice isn't wrong, but the problem was that the world was undergoing an advancement process at the time. Nobody knows what happened, but even the World Origin ended up being locked.
As a result of locking the World Origin, this world could no longer advance itself, being permanently locked at the seventh-tier pinnacle. Or, it should be said, it's stuck between the seventh and eighth tiers.
The world originally was advancing vertically, but now it's developing horizontally.