IMO the goal is a bit different. It'd be just way too much data to track people successfully, even with on-device filtering, especially because everyone with ill intentions would just use non-backdoored devices for their malicious activities.

A much more achievable goal is digging up dirt on specific people and opponents. In the end governments can struggle to justify how they got their hands on info about an affair you had or that you shocked dogs ~~on stream~~.

Such device backdoors are just a get-out-court-free card and a way for the media to justify not asking any serious questions.