Ahh the bad high school maths take, which doesn't account for the risk.

People don't just build 1 thing for a house nor can they afford a $20k failure.

If you take Fred who saves up $10k for a major purchase for his house each year.

If there is a 10% chance of a failure, then Fred will have a 53% chance of bankruptcy in 7 years.

You can't run an economy where everyone is bankrupt.