Certain addresses get flagged in bank and verification systems over time that are shared addresses among many people. Places where someone can get mail without a permanent legal address is one example. Shelters, general delivery at the post office, etc. So much of the concept of your identity is tied to your legal address. Courts can use this too and claim they can’t find someone then issue default judgements against them. Meanwhile, so many places are heavily monitored because they have turned into police states, it is not usually in question for the goverment who someone is and where they are located. The post office should provide long term PO boxes for unhoused people for free and these should be accepted as legal addresses. But often, you’ll find a PO Box isnt accepted.