People are homeless for different reasons. If someone just happens to be down on their luck or having financial trouble after fleeing an abusive family situation, housing seems to work fairly well. However for people with untreated mental illness and addiction, there can be problems. Especially since many of those people would actually turn down a free place to stay (as we saw recently in Echo Park). Maybe we can make more inclusive housing for the homeless that allows large pets and drug use, but the rent you see on those empty apartments is predicated on assumptions on a tenant's risk. Employees people who care about their credit score are going to have a much different risk profile than the homeless.
[1]: Called The Streets Within, part 1 here: https://www.latimes.com/california/story/2019-08-15/the-stre...