In many states, taxes were always owed. I’m surprised they haven’t demanded address lists from every online retailer like they did when they went after online tobacco sales. I wouldn’t be surprised if they did do that eventually.
Well, that is simple to answer. No law. With tobacco there was a 1948 ATF law requiring tobacco sellers to report to the appropriate agency anyone (other than a distributor)names, addresses and amounts spent. They have agreements to collect sales tax.