The Demon Race couldn't reproduce without the help of a Male's soul. They could only bear a healthy child if they swallowed the soul of their partner. This was the way of life for the Demon Race before Lawrend came.
It was also the reason why Aezel and Juju found him. The two tried to have him impregnate them in their own ways.
However, with the return of the Demon World's natural laws, the deficiencies of the Demon Race were likewise fixed. They didn't have to rely on swallowing the soul to give birth to a healthy baby.
These Heaven Demons initially wanted to get Lawrend's favor so they would be able to bear his child once he neared the end of his life or if he somehow ended up close to death.
But since they were no longer demons, this was no longer a valid reason. Furthermore, Lawrend was planning to become a God.