Adopting a child is the process of finding suitable parent(s) for a particular child. It's about matching a child to prospective parents.
The child's needs are paramount.
Maybe that's what they mean by not being allowed to "choose"?
Precisely. My parent's received a picture of my sister long before they even flew over to China. Whether there was actual matching to parent's portfolios though I don't know. It's something that the agencies need to be legally obligated to do. Match both together for the best future. Of course the problem now lies with finding the right indicators that are best to match the two parties.
My mother was distraught when returning to the UK because of worries that my sister would not be 'right'. This sounds awful but it really isn't. She had raised me and my brother and we were a well-functioning family and she never wanted to ruin that. It's easier to think more logically before you actually get into the process of raising the adopted child of course. Bascially, parent's needs must be thought of too, especially where there's already ane stablised family involved. Resentment towards a new sibling that requires much more attention (due to mental/physical illness) will cause more harm than good in a family as a whole.