Local Government and Public Involvement in Health Bill

I do not understand. If local authorities can create parish councils, even as part of any restructuring of a future local authority, unitary or otherwise, it seems extraordinary that the Secretary of State would get involved in the number on that council. Surely that could be left to the local district or county council to prescribe the number? It is really using a sledgehammer to crack a nut to have the Secretary of State involved in the number of parish councillors.