Why did the national treasure panda return to the motherland after being sent abroad for a certain period of time?

1982, in response to the global call for the protection of endangered animals, China announced that it would stop giving pandas abroad from 1982. Later, I thought, I signed a lease agreement and set a fixed number of years. The most important thing is that if a giant panda gives birth to a cub abroad, the property right belongs to China, so the cub should be sent back to China.