I can see that a judge could think, 'the only utterly dreadful, abusive thing they will likely ever do has been done so if I jail them all I do is put a child in care who has mostly loving parents and traumarise her further'.
The only thing a jail term is for in this case is punishment and deterrent to others, which as a society we have moved away from to rehabilitation and individual crime prevention.
Anger doesn't cover the feelings towards these parents who mutilated their toddler. But we need far more intelligent, culturally based education than anything else.