Social workers do their best.
They are overworked and underpaid.
The profit centre philosophy now holding sway requires them to keep as many children out of care as possible, because taking kids into care costs money. If they do their jobs properly they get fired or backed into corners by management scum until they have nervous breakdowns themselves.
They also know that they harm children by taking them into care - and are supposed to balance when the right time to apply is.
Small wonder social work has one of the highest rates of burnout of any profession.