They were self regulated by the tattoo industry. Shops wouldn't sell them to you online or in person without a license or a verified shop claiming you. Then, Amazon started selling cheap, Chinese knock off kits to whoever had access to a credit card.
Some of my highest quality tatts were done by people who weren't certed and hadn't ever worked at a shop. If one was interested in buying a machine, and really wanted one, they were easily available and always have been.