The relationship between Heaven and Earth and a Cave Heaven Blessed Land is akin to that of a modern conglomerate and its subsidiary divisions.
Every Cave Heaven Blessed Land born within Heaven and Earth can be seen as a new subsidiary of the great conglomerate, Heaven and Earth.
If Pei Xuanjing and his fellow True Immortals held the Authority of the Great Ming World, they would be akin to shareholders and board members of this great conglomerate, Heaven and Earth.
Then, the Wielders of those Cave Heaven Blessed Lands, the Sects, and the mighty ones are the shareholders and CEOs of the subsidiary companies.
However, if the evolution of a Cave Heaven Blessed Land is the process of a subsidiary growing and developing, then its transformation into a Small Thousand World is essentially these subsidiaries growing strong enough to become independent, a step towards breaking away from the conglomerate's control.