According to Paula Fredriksen, in From Jesus to Christ, the reason was that Jewish Christians were preaching the imminent return of the King of the Jews and the establishment of his kingdom. To Roman ears, such talk was seditious. Romans gave Jews at that time limited self-rule (see Iudaea Province); the main obligations of Jewish leaders were to collect taxes for Rome, and to maintain civil order. Thus, Jewish leaders would have to suppress any seditious talk. In cases where Jewish leaders did not suppress seditious talk, they were often sent to Rome for trial and execution, or in the cases of Herod Archelaus and Herod Antipas merely deposed and exiled to Gaul.Catholic Encyclopedia: Herod: "He [Archelaus] soon aroused opposition by marrying his brother's wife -- a crime like that of Antipas later -- and having been accused of cruelty by his subjects, "not able to bear his barbarous and tyrannical usage of them", he was banished to Vienne, Gaul, A. D. 7 in the tenth year of his government (Jos., "Ant.", XVII, ix, xiii, 1, 2)."; "Contrary to his better judgment he [Antipas] went, and soon learned that Agrippa by messengers had accused him before Caligula of conspiracy against the Romans. The emperor banished him to Lyons, Gaul (France), A. D. 39, and Herodias accompanied him (Jos., "Ant.", XVIII, vii, 2). Josephus (Bel. Jud., II, ix, 6) says: "So Herod died in Spain whither his wife had followed him". The year of his death is not known. To reconcile the two statements of Josephus about the place of exile and death, see Smith, "Dict. of the Bible", s. v. "Herodias" (note)."
