Because it would prove an incentive for unscrupulous Muslim males to seek out western women vacationers and the like for marriage in order to gain citizenship of western countries. What prompted your daughter to become a Muslimah btw? What form of Islamic garb does she sport?
Ok I have no misconceptions that this no doubt happens in some cases but to condemn them ALL as being unscrupulous by not allowing ANY of them to become citizens is downright discrimination.

My daughter married a muslim. Whether she converted to Islam of her own free choice or whether it was because it was expected of her I neither know nor care. She is an adult and can make these decisions for herself. However she doesn't sport any Islamic garb. She does dress more modestly as in no more low-cut, or see-thru tops since she converted but I'm fine with that too LOL.