Lin Shen also heard an even more explosive story. Originally, there was no blockade between the Ancient Realms and the Celestial Court. Divine Beings from the Celestial Court were always free to enter and exit the Ancient Realms, selecting experimental subjects to bring back for research or as labor.
It wasn't until the emergence of the First Immortal, who used Supreme Power to sever the connection between the Ancient Realms and the Celestial Court, preventing Divine Beings from entering the Ancient Realms, that the people of the Ancient Realms avoided the fate of enslavement by the Divine Beings.
One could even think of it in reverse: it wasn't the Ancient Realms that were sealed off, but the Celestial Court.
The Celestial Court, though vast, is merely a corner of the Cosmic compared to the countless Ancient Realms.
The Divine Beings of the Celestial Court being unable to enter the Ancient Realms is equivalent to being sealed within the Celestial Court.