I don't really, it's just a matter of risk avoidance, paying attention to what happened post-2008 housing crisis, and understanding the consequences of strategic default.
If you don't pay your mortgage, it's generally either impossible or not worth suing you for the outstanding balance. Usually what happens is the bank spends a few months going through the foreclosure process, trashes your credit score, takes your house, and evicts you. This is bad, but if you owe $400k on a house that's worth $300k, it's less bad than continuing to pay your mortgage and dump an extra $100k down the drain. You save up first + last + security + moving costs for an apartment or renting a house out of the freed up cash flow, deal with the fact that getting credit is going to be difficult for a while, and move on with your life.
This description of (individual / personal) "strategic default" is interesting, maybe because it strikes me as a theoretical approach that is extremely rarely employed in real life. Corporations can and do consider bankruptcy a rational option under various circumstances, but -- maybe for a mix of cultural and legal reasons -- for individuals, there's a stigma, a sense of shame and failure, and it's viewed as a desperate measure of last resort.
If you don't pay your mortgage, it's generally either impossible or not worth suing you for the outstanding balance. Usually what happens is the bank spends a few months going through the foreclosure process, trashes your credit score, takes your house, and evicts you. This is bad, but if you owe $400k on a house that's worth $300k, it's less bad than continuing to pay your mortgage and dump an extra $100k down the drain. You save up first + last + security + moving costs for an apartment or renting a house out of the freed up cash flow, deal with the fact that getting credit is going to be difficult for a while, and move on with your life.