SUPER high level, and slightly biased explanation: corporate home buying.

Large investment firms like buying up property increasing the demand and raising prices. This prices normal people out of being able to afford a house. It also raises other housing related costs like rent, because these firms want to make a profit. This in turn prices people out of being able to afford ANY housing.

When we’re just numbers on a spreadsheet, there is a certain level of vacancy and homelessness, that maximizes profits.