I think that you are looking at it wrong.
The state prioritises housing families with children and always has done. A singe person can accommodate themselves much more easily - they can share a house, get a bed sit or whatever.
The "Mortgage to Rent" scheme is designed for people who have an unsustainable mortgage whose housing needs would be met by the Local Authority if they were homeless. The Housing Group/Local Authority looks at their current home. If it's what they would be getting anyway, it makes sense to leave them there and have the state pay for it.