Universally known to whoever wanted to intercept that traffic.

Maybe and hopefully not known to the staff of those networks (the current staff could be maintaining what somebody else set up) as some of those companies fixed the problem when contacted by the researchers.

For sure not known to me and a lot of other people. I believed that everything in digital streams was encrypted. Ok, those ATM connections are probably tech from the 90s, but they probably had upgrades in part because of regulations. Privacy, security, nothing?

Correct, this is why HTTPS (and encryption in general over the network) has become so popular. This property of traffic being intercepteable is also present in cable traffic as well, it's not hard to intercept traffic, you just find a tap, plug in a cable and observe, it's not even obviously illegal, there are many legitimate reasons to plug in a cable in a tap in the public, so there's a lot of possible alibis.