Once involved, social services have a duty to ensure the welfare of the person they are called in to support. It doesn't matter who involved them, the duty remains the same.
Let's say for arguments' sake that the hospital calls in social services because they don't believe that a patient is capable of looking after themselves. Does this patient have the mental capacity to choose to live with their family? What was the family doing beforehand - have they always supported this patient or are they only interested now there's the possibility of selling the house? In other words, is there the possibility of abuse (financial or otherwise)? There have been a few cases in my area where the possibility of neglect, financial abuse and physical abuse has been investigated. In most cases, it's down to misunderstandings. But, occasionally, it isn't.
If social services did not stay involved, and something went wrong, we would all criticise the social worker for ignoring the signs. If they stay involved, then they are being busybodies. They cannot win. Lord knows I have little time for some social workers, but they do have a responsibility and it's good that sometimes they do carry it out.