I was reading about The Hacking Team on Wikipedia. It produces "offensive intrusion and surveillance capabilities" and sells it to "to governments, law enforcement agencies". Its spyware allows governments "to monitor the communications of internet users, decipher their encrypted files and emails, record Skype and other Voice over IP communications, and remotely activate microphones and camera on target computers".
I hypothesize that the government would install such spyware on the PC of users suspected to be involved in illegal activities. This would allow the government to trace the illegal activity, collect evidence and finds co-conspirators.
But I was also reading this answer. If a government wants to track an user's traffic, and intercept the traffic from and to the internet, it looks like it simply has to announce on BGP a new routing path to that user IP address. That new path would be more specific than the existing path, shorter than the existing path, and it so happens that it goes through the government's servers.
So why governments engage in installing spywares when they could simply re-direct the user's traffic to their own servers?