John Bloom from https://www.desiringgod.org/articles/why-was-judas-carrying-the-moneybag
For a long time, Judas’s reputation was as a student and close companion of Jesus. Judas lived with Jesus and the other eleven disciples for the better part of three years. He traveled long, dusty roads with these missionary comrades. He ate with them, sat around evening fires with them talking about the kingdom of God, and he prayed with them. He heard more of Jesus’s sermons than almost anybody. He received personal instruction from Jesus. He witnessed Jesus’s incredible miracles and saw the Father provide for their needs over and over again.
All during the time Judas was part of the Twelve, he mostly said and outwardly performed the right things. It’s astonishing that none of Judas’s fellow disciples perceived his deceitfulness. Even when Jesus finally sent Judas off to carry out his betrayal, the others didn’t seem to suspect him (John 13:28–29). It was a stunning and grievous blow to them all when in the end he sold Jesus for thirty pieces of silver (Matthew 26:15).