Why did Emperor Wu pass it on to Liu Fuling?

Liu Fuling grew up smart and knowledgeable, tall and strong, and was very popular with Emperor Wu. The original prince Liu was killed, and the position of the prince has been vacant. Emperor Wu of the Han Dynasty wanted to make Liu Fuling a prince, in order to avoid the recurrence of Lu's rebellion and to facilitate the death of his mother Zhao Jieyu (Mrs. Gou Jian) in 88 BC. In the second year, before his death, Emperor Wu of the Han Dynasty named Liu Fuling as Prince and appointed Huo Guang as General Fu.