Because we do not yet have enough of them to satisfy the demands of our government's policy.
You gotta go back to the immigration policies that were hatched by the policy wonks in the administration and Congress which set in place policies calling for intentional diversity/multiculturalism so that the U.S. population would more accurately reflect the world, i.e.: so many percent African, Asian, Muslim, Buddhist, whatever, etc. Those policies were fine-tuned and nurtured under Clinton, and now the chickens are just starting to come home to roost, so to speak. The "Balkanization" of Amerika.