> Since you seem to know about the subject, how are these not immediately found and shut down?

Because - depending on cell tower coverage and the antennas installed on it - the degree of precision is far too low to be useful. In rural installations and the worst case, aka a tower with a dipole antenna on a mountaintop, at 900 MHz the coverage will be around 35 km. Segmented antennas just limit the section of the circle where the endpoints are. In suburban areas, coverage is usually 10-20 km, and urban areas it's 5km and less.

Now you know which cell and cell section the user is in... but to actually pinpoint the user? That takes some more work. First, you need a few more towers that the user can reach for triangulation - the more the better - but if the operator of such a setup is even remotely clever and the hardware/firmware supports it, they will have locked the devices to only connect to a single tower (you can see a map at [1] that shows the IDs). If the operator didn't do that but the site is too remote to achieve triangulation, you might need to drive around in a van and use an IMSI catcher, aka a phone tower emulator, and hope that eventually the site's devices register at it. That, however, is a lot of awful work, and is often not legal for police authorities, only for secret services.

Now you might ask yourself, what about 911, how can they locate callers precisely? The thing is... it depends. Landlines and VoIP lines are usually mapped to a specific address (which is why VoIP providers give you an explicit warning that, if you do not keep that record up to date, 911 calls will be misrouted!), so that's trivial. Mobile phone callers however, until a few years ago the degree of precision was exactly what I just described - it completely depended on celltower coverage, with the only caveat that a phone will connect to another operator if it shows a stronger signal for 911 calls. Only then, Android introduced Emergency Location Service [2] and Apple introduced Hybridized Emergency Location [3] - these work with the sensors on the phone, most notably GPS/GLONASS/Beidou, but also SSIDs of nearby WiFi APs and specific Bluetooth beacons. Downside of that is, of course, the 911 dispatch needs an integration with Apple and Google's services, users can disable it for privacy reasons, and older phones won't have anything - so in these cases, 911 dispatchers are straight out of luck and again reduced to the above range of precision.

[1] https://opencellid.org/

[2] https://www.android.com/safety/emergency-help/emergency-loca...

[3] https://www.apple.com/newsroom/2018/06/apple-ios-12-securely...