Peter, not to be able to differentiate between principle and detail is a bit like not being able to see the trees for the wood.  
 
 
The detail here we shall never learn. i.e. the circumstances that led to there being, on file, a comment from a Judge regarding the importance of ethnicity in the fostering process.
As to why the comments of a Judge took precedence over a common sense approach is a symptom of the present new-age methodology which itself supersedes the historical practices that were found wanting some thirty years ago.
That the fostering habit, such as it is within the indigenous population, has not kept pace in the various ethnic groups with their own spawning of 'orphans' is, I am sure all would agree, not the fault of any child.
What was the alternative path here?
Rotherham SS could have stuck to it's guns and continued fostering in this one particular household and prioritised the care and nurture of these children in defiance of the courts wishes? 
We may all of us wish that it were so, and yet none of us can know the circumstances that brought this case before a Judge in the first place.
Happily, the children are still together and receiving excellent care, we are assured.