You're describing a "heads I win, tails you win" situation with no down payment. If the house drops in value, the borrower walks away and "wins". If the house a

You're describing a "heads I win, tails you win" situation with no down payment. If the house drops in value, the borrower walks away and "wins". If the house appreciates in value, the borrower stays and the bank receives X% interest, on time, in full, for 30 years and "wins."