MineralWater Its not, in the UK for example, they use CCTV to track users if they need to, they can also get logs from ISPs etc, a hash is a terrible method of tracking someone through places, especially when you have as many cameras as the UK does, plus cell towers, free wi-fi so on.
You triangulate when tracking a user, cell towers are excellent here, 5G allows you to triangulate down to I believe meters, if not closer, 4G couldn't do this, you can then link them to a place by using CCTV.
A hash is good when you have a static piece of content like a video or image (say CSAM) and you need to compare it as it is "known", its a very quick, easy way to know it exists.
AI does play a part also, it is used with CCTV systems, more now than ever.
But I agree with your statement, we shouldn't need scanning at all ideally as CSAM or any abuse material shouldn't exist, but sadly it does, but then another excuse would be made in its place.