REO or real estate owned is the term for a bank holding a property.
A bank is exempt from paying municipal property taxes so they try to hold them until the market rises. If a bank ever sells a foreclosed property they must recognize the difference between the original loan and the sale. A loss factors in to how they must calculate the banks solvency. They have no incentive to put property on the market other than the maintenance fees.
This article seems to be trying to stir the pot of generational warfare. A better Target would be empty houses that banks won't sell at market prices.