Well actually the reason was different
Back in the 1980s, you had "The Phone Company", and only it could get access to SS7. Authentication made no sense as this was the time before public key cryptography so you could easily just sniff any password anyhow and even shared key cryptography would have been expensive. Also there was no reason for it, as "The Phone Companies" of all countries trusted each other.
Today there's lots of phone companies with access to the SS7 network. They shouldn't sell that access... but there are some that apparently do. After all there are plausible things to do with access to the SS7 network, for example operating SMS gateways to the Internet.
This story actually highlights another problem, and that is that SMS is completely unencrypted, except for the last air interface from the tower to your mobile phone. It never should have been used for anything even remotely resembling security.
Biting the hand that feeds IT
