The reason it isn't already a thing is because it would require a law on the books across all scales for business records with compliance costs - down to Billy

The reason it isn't already a thing is because it would require a law on the books across all scales for business records with compliance costs - down to Billy Bob's Billboards where he takes cash for ad postings. The legal system is still based on assumptions of the government not having default access to all financial transactions as not only would it have been just useless abusable spam but it would have generated massive expenses for little gain and drawn considerable ire. Plus said proposal would trigger every Revelations literalist about "the number of the Beast" as well as privacy advocates and businessess upset at increased compliance costs and liability. Until the Fake News rise approaching moral panic absolutely nobody would be for it. Hell if they were to try to codify such requirements it may not even survive the supreme court.