I’m thinking this is because of the new bankruptcy laws that make it more difficult for CC debt to be forgiven more so than mortgages. Change the mortgage rules and relax the CC bankruptcy rules, and you’ll have the opposite problem.
I kinda doubt that’s the reason. This would require a level of knowledge of bankruptcy laws which most people don’t have.
More likely, homeowners who didn’t put anything down don’t really care if they lose their house or not. I bet people who put 20% down aren’t so nonchalant about losing their home.