Mainly because the governments already have access to everything and I mean EVERYTHING.
There’s limits, largely around the speed and accuracy by which data can be ingested and processed. You can look for everyone somewhere sometimes and someone everywhere sometimes and someone somewhere at any time, but it takes a ton of digital resources to monitor everyone everywhere all the time. For the data to be meaningful it has to be interpreted.
Manned checkpoints allow local state actors to make decisions in near-real time relative to immediately present information. The classic example is someone with a stale warrant or notice on their record. The sheer volume of delinquents makes pursuing every individual troublesome, but as soon as a known offender steps across a checkpoint the police can pounce on the individual offender in that instance. If you’ve got a five year old traffic ticket, a police officer can be in your face about it as soon as they run your ID.
If the first thing Donald Trump did in office was arrest every Cheney and toss them into Gitmo, I would feel significantly less bad about him winning the election.
He won’t. And that’s one more reason why he fucking sucks. This is all just theater, before the Cheneys are back to cutting the GOP checks for special O&G industry favors.