Part of the problem is that professionals like social workers start off working with a family to support them with their parenting. It's all about building trust with the parents and having a good relationship with them. That makes it hard for them to suddenly recommend that the children are removed.
I adopted two children who were seriously neglected. They had huge files - just about everyone day another neighbour, teacher, medic, family member even contacted social services with yet another concern, and it was simply just added to the growing pile.
The birth parents were actively avoiding the social workers too. They were never at home for visits.
But the social workers kept ploughing on with a "be nice" strategy to get the birth parents on side.
I said before, it's only when there is a catastrophic incident that anything is done.
I have the minutes of the meeting where my girls were taken into care. There were 14 professionals round the table at that meeting - social workers, teachers, nursery staff, paediatrician, GP, police, health visitor....the threshold for removal is high, often involves lots of agencies, and is seen very much as a last resort
If there is no catastrophic incident, they just keep giving another chance.