To take a different perspective on this - why would it make sense to subsidize the purchase of larger than necessary homes because they're able to lock in low r

To take a different perspective on this - why would it make sense to subsidize the purchase of larger than necessary homes because they're able to lock in low rates for a lifetime? It would make far more sense if homeowners had more skin in the game, and had to make rational choices about the size and location of the home they purchased.