A social security net which doesn't cover mortgages is by definition useless for everyone who has a mortgage. That's a significant part of society. So, a social

A social security net which doesn't cover mortgages is by definition useless for everyone who has a mortgage. That's a significant part of society. So, a social security net which doesn't include this is more of a social security black hole with a few ropes, only useful for people who have some weird "model life" (e.g. a student without anyone who depends on him) and not for normal people. Usually this goes against the stated goals of social security nets which are introduced to allow people to take risks which could be useful for society without ruining their lifes in case of a failure.