Also, remember that SS7 was developed in an era when there were highly controlled networks often run by a single monopoly provider, or a very select few telcos.
An era when there'd be tons of players and open competition wasn't really something that is likely to have crossed the minds of telecommunications engineers in the 70s/80s.
This is Ma Bell, Euro PTTs and Telecom companies stuff.
Security was all about having a good lock for the exchange building.
Biting the hand that feeds IT
