Because they are buying up stocks of that limited housing and holding onto it for rental income and capital gains. Previously, that had been off-limits as part of a generational wealth building process for regular families. Now more houses will be rentals and that money will compound capital for investors. By definition that further concentrates wealth.
We need more low cost apartments and condominiums that are close to jobs. Low wage workers are being expelled from urban areas because they cannot pay rent, and are forced between living in slum like urban conditions or paying high costs to commute from distant affordable areas. Corporate ownership of housing won't solve their issues, solve zoning issues, or increase housing starts.
edit: "off-limits" to the extent homebuilders could make a profit and lenders could make a profit, but not excessively.