>When you buy a house, the mortgage is associated with the buyer, not the house
In the US, this depends which state you are in:
https://www.investopedia.com/ask/answers/08/nonrecourse-loan...
The non recourse states are Alaska, Arizona, California, Connecticut, Idaho, Minnesota, North Carolina, North Dakota, Oregon, Texas, Utah, Washington.
>and you can't just dismantle the house and sell it for parts to cover payments
You can do this in every state, at least with a conventional mortgage. If you default, they can pursue your other assets, except in non recourse states.
>we'd have a lot of on-paper debt associated with empty lots that mortgage holders could simply walk away from (perhaps after a nominal sale)
I don't know what "after a nominal sale" means, because if you sell a property with a lien on it, then the lien holder gets paid first. And underwriting would not let people who have a history of dismantling a house and defaulting borrow money over and over, and people need a place to live, so I'm not sure why anyone would take out a mortgage to dismantle a house. The scenario makes no sense, as raw materials are cheap, and labor costs are expensive.
> It's preposterous, they'd never let that happen. So, why with businesses?
Because the lender agreed to those terms. No one forces a lender to lend money without a personal guarantee.
https://www.investopedia.com/terms/p/personal-guarantee.asp