There could be a lot of reasons why not. There isn't enough "real" evidence to remove them. If the mom was lying about being drunk and passing out, there would be no evidence of neglect. There is no actual proof that Lisa wasn't abducted. If she was, the parents couldn't help that, at least not at that moment.
Also, the children, up until now, have been living in a house where there were other adults, presumably responsible adults, so why take them out of there and place them in unknown territory? They were safe where they were and also, consider the turmoil these kids have already been through. To take them away would definitely add to that.
Other than the missing baby, I don't think there have been any signs of abuse or reason to remove them. The parents not letting LE interview isn't really grounds for removal.