Let's say Joe buys a house for 800k, then discovers he can't afford it. He puts it on the market, and learns he cannot sell it for more than 500k. Assuming he put 20% down, his mortgage is 640k, so he comes up 140k short. What's wrong with the bank holding his note at the rate he was paying on the mortgage?
If he was paying 5% on 640k = 32k a year (in interest). On 140k @5% 7k a year. Surely he can pay that and have money left over for rent? (He also gets out from under property taxes of probably > 12k and insurance of probably > 4k. So his cash flow, which is the problem, increases by 41k a year.)
Why do the rest of us have to bail him out by reducing the principal and / or the interest he pays just so he can continue to live in a house above his standard of living?