How can increased housing prices create foreclosures for the people who have been living in the area? If housing prices double overnight, the mortgages don't ch

How can increased housing prices create foreclosures for the people who have been living in the area? If housing prices double overnight, the mortgages don't change a cent. The only way Google can create foreclosures is that they create unemployment. That doesn't seem likely. Getting more wealthy engineers to an area will likely increase jobs.