Birthmothers sometimes back out. Hell, it is THEIR baby. Amazing how entitled some people get about other people's children.
I would rather have a raft of birthmother's back out on me than take children from countries who dont let their mothers have a choice and keep their babies. There is a big difference between a mother who chooses to place her child for adoption and a mother who has no choice. Continuing to adopt from these countries (if you have) supports a sick, tyranical system, and prevents change.