There are definitely pill mills in the poorer parts of town. And usually poor populations receive Medicaid, which will typically pay for the stuff. Just anecdotal evidence as a pharm tech in a rough part of town during college, but after a while we had to actually stop taking scripts for most pain meds (still got a ton of people using trazadone and stuff, though) because the pharmacist just didn’t think it was worth his license if the scripts were tied back to a pill mill.