North Korea surely has contacts with the rest of world, to deal with China, for instance.
They tell you about North Korea and your radioactive future. You like big problems and give it your best effort, perhaps thinking that you had a small part in saving the world. Then one day you read in the New York Times that your well intended project doesn't just scoop up communications from North Korean thugs, but what you helped make is collecting communications on everyone. It's helping the DEA illegally bust people. It's helping diplomats illegally snoop on our allies. It's helping keep US companies aware of what non-US companies are doing. Etc etc.
tl;dr Anyone could be a terrorist, everyone must be monitored.
What would your collection proposal be then?
You can't determine data of interest until you have sufficient data to determine if it's of interest in the first place. Even the NSA doesn't have an Oracle computer that can look into the future and figure out what vanishingly small percentage of communications are just the ones they should be interested in. If they did, they could also solve the halting problem and rewrite the history of computer science and time-travel.
Remember, the standard the NSA is held up to is that it should not only be following known bad people who are/might be doing bad things, but to ferret out the unknown bad people. Every time there's a Boston or similar, everybody goes and climbs all over the NSA for "not knowing about these guys"
You can't do that until you have a sufficiently large enough collection of unevaluated data to start looking through.
I'm not saying it's right or wrong, only that it's the reality of the task spy agencies have before them.