The Looming Tower is a Pulitzer Prize winning nonfiction book by Lawrence Wright about the people and motives leading up to the 9/11 terrorist attacks on the World Trade Center in New York.
In the book, terrorist recruits are described as follows:
What the recruits tended to have in common... was displacement. Most who joined the jihad did so in a country other than the one in which they were reared... they had little standing in the host societies where they lived. Like Sayyid Qutb, they defined themselves as radical Muslims while living in the West... alone, alienated, and often far from his family, the exile turned to the mosque, where he found companionship and the consolation of religion.
(Wright, The Looming Tower, Google Books)
As in any culture that is different, people tend to gather with others of their own type. Since these recruits have a shared antipathy towards Western culture, and since they are inclined to gather with each other, it was easier to indoctrinate them for the jihad's purposes. Displacement is a powerful tool in molding a person's ideology, and in this case, it was used to great effect; the recruits only needed a little nudging to become full "radicals" and start believing in jihad. In a more general sense, recruits could not fully embrace the jihad while living in the West -- the "near-enemy" was too close to their own experience. Once recruited and living in the East, surrounded by like-minded people and charismatic leaders, they could be fully taught to hate the "far-enemy." Distance allowed them to forget or ignore their previous lives and focus entirely on the jihadist mission, and so the "far-enemy" replaced their personal experiences.