We have a similar issue in the UK since there are large houses being occupied by older couples whose children have left. Since annual property taxes are low (~4k - we call it council tax) and tax on buying property (stamp duty) is high, there is no incentive to move to a smaller place.
The UK's problem is not so much lack of houses (although the planning system really doesn't help) as a combination of over-financialisation and over-centralisation. People believe that all the high-paying employment, entertainment, and oligarch money is in London. It's also the default destination for immigrants. As a result you've got people trying to live in sheds there. Meanwhile everywhere from seaside towns to Birmingham gets treated as second-class citizens, with inadequate public transport and little inward investment.