They will be limited in how many targets they can process. Snowden revealed 2 degrees at the time. So if a person interacts with 100 people over a year, that is upto 10,000 people to investigate for one person of interest. That's a lot of manhours for a single target. Likely that's the worst case, and they must also have ways to triage.

But you are right, they cannot spy on ALL of us, or even a significant number. Too much shit, lol