I am not here to nit pick about this post, but this made me think:
> owning a lot of houses is not a good business
Generally, I agree. What do you think makes commercial (office) buildings different? Probably 90% are owned by insurance companies, private equity, and pension funds. My guess: Scale matters. Also, maybe I am blinded by big cities, but second tier cities and below might have lots of small fry landlords that own one or two small commercial buildings