There are still requirements to participate in the Section 8 program though and a landlord could easily make sure they don't pass the government's inspection.

Section 8 is a mixed bag. For "professional" landlords who have a bunch of properties and understand the system well it can actually be great. Guaranteed payment, often highly stable tenants who rarely move, there are pros to it. OTOH for small-time landlord it forces you into a three-way business arrangement with the government and your tenant that can be a huge hassle. When we considered landlording there was no way I would've dealt with Section 8 tenants.