I did EDI work for several major national and international companies you've definitely heard of. This is all too common, we're talking about millions of dollars of transactions per day flowing over insecure FTP sitting on the internet. VANs, originally used dial-up modems to deliver EDI, now they often use insecure FTP.
A few brave companies have tried to put their FTP systems behind VPNs, but the momentum is hard to overcome. What is more popular is firewall rules that only allow large blocks of IPs owned by other vendors they deal with. It is good in theory, until you see how large/diverse some of these blocks are (e.g. all of AWS's Eastern data center).
It was a very loud wake-up call seeing what inter-business stuff looked like. It is the wild west or a flashback to the 1990s security wise.