According to the Census there are a lot more empty houses than homeless people. Let that sink in and you start to realize all is not what it seems.
This particular statistic needs to be handled carefully. There are problems with both its definition and its nature. Empty housing has a fairly broad definition that includes housing that is unfinished, in the middle of repairs, or unfit for habitation.
The nature of housing with relationship to homelessness depends a lot on where the homeless people are and where the housing is. Empty housing in towns and cities that are depopulating is unlikely to be all that useful. Simply taking people from cities with high levels of homelessness, ripping them out of their communities, and plopping them down into communities that other people are leaving is not a favor.
Also, you shouldn’t just warehouse unhoused people in whatever housing is available. Many of them have mental illnesses that need good access to mental health services, transit, and jobs. Just because they’re under a roof doesn’t mean the job is done. The housing should be tailored to the various populations that it will be serving.