Slumlords who don’t want to keep their property up, who might be just holding the property to sell at a later time ... those landlords love Section 8 housing. It give them income with minimum upkeep on their part.
If they wanted to take care of the property, they could get higher rents.
You are right. If they can get a better long term return by fixing and maintaining the property, why rent to Sec 8 tenants?