The reasoning I am always given is that houses are built using very inexpensive materials and aren't expected to last more than 30 years, so they either need to be renovated, a process that companies charge almost as much as a new house to do, or destroyed. My reply is that houses in America are often built cheaply too and usually given a lifetime of about 40-50 years, and problems usually crop up long before that, but we usually fix things as we go and keep pushing the life of the house as long as possible. To that I am often told the earthquake code reason haha.

I think it's more likely that it's just been this way since the war, so many Japanese people think this is how it is, and as a result the idea of living in a used house seems strange and no one wants to do it. I do think this idea is slowly changing. Building a house is becoming more and more and more expensive, as inflation is hitting here very hard. Many people find they can't afford to build a house anymore, so a secondary market is starting to pop up. It may be another generation before used houses become more common, but the change is starting to happen.