And it's been going on for years. Years ago, when I had a landline, I started to notice that a lot of spam calls came from the same area codes and prefixes. A quick trip over to telcodata.us showed that all of these prefixes/thousands blocks were assigned to the same company, which had a web storefront as a wireless provider but didn't really provide cellular service. Apparently, nothing has changed.
They are created/supported by the robocallers.