Complex sentence: Japanese-born people of Korean ancestry are considered resident aliens because of their nationality and are often shunned in legitimate trades, and are therefore embraced by the yakuza precisely because they fit the group's "outsider" image.
Split into simpler sentences: Japanese-born people of Korean ancestry are considered resident aliens because of their nationality. Whilst Koreans, who are often shunned in legitimate trades, are embraced by the yakuza precisely because they fit the group's "outsider" image.