Pilate asked this because he understood clearly that the religious leaders had delivered Jesus over to him because of envy, not because of any real crime.
For he knew it was out of self-interest that they had handed Jesus over to him.
NMVThis was because Pilate [armed with a spear] knew that due to hatred without cause he had been taken.
OJBFor Pilate knew that because of kinah (envy) they had delivered Yehoshua up.
TCENT(For he knew they had handed Jesus over out of envy.)
T4THe asked that question because he realized that the chief priests wanted to have Jesus executed. They had brought Jesus to him only because they were jealous of Jesus. And Pilate thought that the crowd would prefer that he release Jesus.