There are a lot of cars, insurance telematics devices, security alarms, etc. sitting on mobile phone networks generating signaling and consuming radio resources. They were designed in the early days and largely not reachable. Simply terminating the credentials in the network doesn't help - it actually makes the problem worse because the firmware on the device is often quite aggressive and keeps trying to attach.
This is something that has absorbed a lot of my time combating and there are efforts in standards bodies to address. This approach actually a pretty good idea IMO.