I've always wanted to adopt a child, and China has an overabundance of children to be adopted. Unfortunately, according to Ma Lei's research, a weird fluke of the law makes it illegal for us to adopt — and believe it or not, for once I at least provisionally agree with the Chinese government.
It's quite easy for a Chinese/Chinese couple to adopt a Chinese baby. It's a bit harder, but still legal, for a foreign/foreign couple to do so. Unfortunately, a Chinese/foreign couple are legally barred from doing so. The reason a concern about abandonment.
A Chinese/Chinese couple are pretty likely to stay put and raise a child, so the adopted infant won't be thrown back into the adoption system. If the adoptive parents have some horrible intentions in mind, they will still be living in China, and therefore theoretically subject to being found out and punished by the Chinese authorities. (Not that legal enforcement is ideal in China, but that's another issue...)
A foreign/foreign couple is likewise in a sense stable. They will presumably be taking the child out of the country, which raises the bar for scrutiny of their intentions, means of support, etc., but they will be doing so together as a couple.
A Chinese/foreign couple, on the other hand, has a certain built-in risk that the other two pairings don't. If they divorce, it's likely that the Chinese partner (usually the woman) will return to China while the foreign partner stays in his home country. The adopted child's support network is therefore also completely sundered, and its status is in question.
If she lives in the foreign country, she will do so without a mother to take care of her. The Chinese, even more so than Westerners, automatically assume that women are better parents than men. Furthermore, the father would be raising the child without any break or assistance from the adoptive mother. While this is obviously possible, it's clearly not an ideal situation.
If she returns to China with her adoptive mother, she will most likely have little financial support. Foreign "deadbeat dads" are a notorious phenomenon even when dealing with their own biological children, and the Chinese government obviously has no means to extract child support from a foreign national living in his home country.
(Those are the problems of more or less honest cases. I'm leaving out the consideration of very real and truly evil scenarios in which a foreigner with horrible intentions bribes a Chinese woman to stand-in as his wife, never intending for her to go to his home country in the first place. It's sad to say, but Chinese law must take into account even the most horrible possibilities, because they will happen.)
The above is not say that I definitely agree with this policy. I am inclined to disagree with it, but I at least understand the rationale for it.
If I were the one writing China's adoption policies, I would want to know some more factual information: what is the divorce rate among Chinese/foreign couples? What actually happens to adopted children in those cases? Is there another way to guard against the potential problems without depriving orphans of loving families? Odds are, the policy was formed on the basis of unsubstantiated assumptions and anecdotal evidence, rather than good social science.