I guess it's for much the same reason why many people would much rather keep a dead relationship going than break the relationship off in the hope of starting a much better one with someone else, or even just enjoying life alone. Call it unhealthy attachment borne out of one's fear of the unknown. "Sure, he treats me like ****, but if I leave him, I may never find another man who will love me." Irrational? Absolutely! But this fear is very real to the person suffering it, and many--it's not just women--are paralyzed by this.
That's my point exactly. One doesn't have to be from another country or culture to feel the irrational fear that keeps people in horrible relationship situations. There are thousands of native-bornAmericans, both men and women, who are in abusive relationships out of fear, especially in "middle America". Demetrios G. mentioned he lives in NYC, where people actually do have far greater access to services for the battered.
Most of America doesn't.