Comment by bluGill

Children in foster care start off in a much worse situation than average. Or at least that is the normal case, there are exceptions like the article.

Many parents of 'mentally disabled' kids put the kids in foster care because the parents need a break from the constant care of a kid who isn't normal. Many other kids end up in foster care because they have been abused. Both of those will make the kids much worse than normal and thus much harder to care for.

Kids that are close to normal but end up in foster care often end up adopted fairly quick - there are plenty of families who want a kid but not their own (I personally know several people with genetics they don't want to pass on - there are other good reasons to not want someone else's kids) - but they will try to select a kid who is going to be easy to raise thus kids who will end up normal don't spend much time in foster care.