While it may seem wasteful to live in a big house, when children or a partner has moved elsewhere, or died, there may be a lot of sentiment in that house.
So the bedroom tax should have some flexibility to allow a person's life conditions to change. A large house is expensive to maintain, so people will move into a smaller house in time.
Governments should NOT be involved here. There are also extenuating conditions, linked to disability problems, that are special cases. Theresa, show some humanity.