Because the Jews were waiting for the messiah and Jesus was a jew.It was the jews who had acused jesus of claiming to be king and they used this to condemn him saying we have only one king.So Pilate gave Jesus this title to befit the Jews allegations.

Many of these people lived in sin and therefore were luciferian more than followers of God. satan hated Jesus and contempted man to slay Him. Many of these people were non-believers although Jesus performed many miracles and spoke in a holy manner not of man. Many of these same people also did not want to follow what Jesus preached becuase they were too involved in their sinful ways and the ways of the world. They basically didnt want to admit to there faults and have someone pointing out there wrongdoing since to change to unsinful ways would mean they would have to stop  doing many of the things they enjoyed.