The thing with a boarding house is it's not targeted specifically at people who are currently homeless. It's just for anyone who wants to save money on housing. Maybe people who just moved to a new city and haven't found a place to live yet, or people who are just starting out and not making much money. It gives them a place to live before they become homeless.

It would also usually have the landlord living there, and they would be invested in the place because it's their source of income, so they aren't going to tolerate people smearing crap all over the walls or tearing out the wiring to sell for drugs or ranting and raving all night long.