> But most of that has been obsoleted by modern cryptography.

Except that people are people, and people make mistakes, and it doesn't take a lot of mistakes to fail in your opsec, and then your whole plot unravels.

Criminals are going to get caught all the time, some even want to get caught. The window of opportunity for network forensics to be an important role in that has been closing and continues to as cryptography and technology advances at a blazing speed.