A corporation can have economies of scale, which could (in a free market) mean lower costs to renters, and also be less subject to the landlord's personal circumstances, which should make rental agreements more stable.

Obviously the property market isn't functioning like a free market, but why do you think that having more private landlords would make things better?

Do you just want a limit on the share of the property market in a given location that one entity can own? That would definitely make sense.