Because the Brahma King knew very well that Buddha really did not want to stay on this planet. The beings here were so stubborn, so covered with ignorance and wrong concepts, so very difficult to teach. So, He just looked around in the whole world and feeling that it was a waste of time so He wanted to go, truly go to Nirvana. So after the Brahma God came down and begged Him to stay already, He still said the same thing. Remember? So, the Brahma continued to persist, persist. “Remember, remember, remember You did that. Remember You did this, just for one stanza, just for one sentence of Truth. And now You’ve already attained Buddhahood, why do You want to leave? Why You don’t remember why You sacrificed?” So, he kept continuing telling similar stories.