Both boarding houses and SRO hotels were put out of business by various government laws and regulations. For example, boarding houses had to pass safety inspections, their kitchens had to meet commercial health standards, the owners had to rent to males and females, and on and on ...
When I was a little boy, the finest meal I ever had was from two old ladies cooking in their home (a house? I was very young) and serving men at a huge table, it was home style where you passed the large bowls and the platters to each other, and at least one of the stoves was in the same room as the table, the best cooks in the world, “grandmother cooking” of the forgotten past.
Back then my dad tried to explain that if you bought a place to live, look for one that could serve as a boarding house, for additional income.