> why would serious criminals continue to use any of these services?
For the same reason they use cell phones which are easily monitored - it's how the bad guys you're dealing with are already accustomed to communicating.
You have to get pretty high up on the chain before encountering a criminal who's taking any real steps at counter-surveillance.
However, an issue for the FBI is that while the big telcos have back doors in place, companies like Tango, Text+, etc do not, making it a pain in the ass to monitor/identify those criminals who at least take that step to duck law enforcement.
For the same reason they use cell phones which are easily monitored - it's how the bad guys you're dealing with are already accustomed to communicating.
You have to get pretty high up on the chain before encountering a criminal who's taking any real steps at counter-surveillance.
However, an issue for the FBI is that while the big telcos have back doors in place, companies like Tango, Text+, etc do not, making it a pain in the ass to monitor/identify those criminals who at least take that step to duck law enforcement.