The Monkey King was crushed under Wuzhishan Mountain. Why did the Jade Emperor and Tathagata lie to him?

Wukong and Tathagata bet that if Wukong can fly out of Tathagata's palm, then Wukong can replace the jade emperor. If you lose, you must obey control. Then Wukong flew out with a somersault cloud and saw five huge pillars (these are actually five fingers of the Tathagata). Wukong thought he had reached the horizon, so he wrote a few words on the post and flew back. For Tathagata, he has flown to the horizon. This is the Tathagata showing Wukong the palm of his hand and the words on his fingers. Of course, Wukong didn't believe it, thinking that the Tathagata was playing tricks. So Wukong said that the Jade Emperor and the Tathagata lied to him. Then he was crushed under the Wuxing Mountain for more than 500 years until the Tang Priest rescued him.