Because that's how you get the haves taking even greater advantage of the have-nots, to the point of injury, illness, and death in the name of slightly greater profits.
By lowering acceptable living standards, the haves, aka the landlords, would be able to cheaply produce bottom of the barrel, barely acceptable living spaces and then since there is a housing crisis they could charge a premium for the have nots, aka the renters, in order to live in those shitty, barely acceptable homes.