My guess from the outside, is that none of these actions are actually meant to "capture" or even "detect" any of those things, the methods are likely to inefficient and small to be able to do so.

What they're trying to do, is make those people not even consider going to the US in the first place, because they're scared of getting caught. Same as a lot of the ICE actions and other things going on. They're not meant to be efficiently solving some concrete issue with their action, they're meant to scare the rest of the populace into being docile and accepting more and more control over time.