Each phone takes time to be detected, identified, and tampered with. So it may make sense to activate a new burner phone, talk about something sensitive, and destroy it right afterwards, before the law enforcement understands what phone was that.
When I worked in a wireless repair shop in early 2000's, we handled the local FBI field office account. Field agents would come in and I'd chat them up as they sat and waited for me to fix their phones.
This was also around the time remote meth labs were getting really common out in rural areas. Multiple agents were talking about how frustrated they were with getting access to burner phones since most of the companies were resellers. They said by the time they got a warrant to start recording the devices, they were already dead.
I guess the bad guys knew their burner phones were only good for about two to three months tops. That was usually the timeframe from when the FBI got a read on a line, saw a judge and got the warrant processed, to contacting the carrier and getting access.
Sounds like whatever was hampering them in the past has been fixed.
That's not really a problem when intelligence services can just "remind" any would-be annoying congress person that they have endless amounts of data showing exactly what they and their family members have been doing and could plant whatever they want into the data they already have.
One of the things that finally convinced Snowden to give up everything he had in order to tell the American people that the NSA was violating their constitutional rights was when he watched NSA director James Clapper outright lie right to the faces of congress. After the truth came to light, do you think Mr. Clapper faced any meaningful consequences for that? Nope. Can you guess why not?
Intelligence services are too powerful to be held accountable by anyone. They'll do whatever they want.
