In short, Crisis was a fanboy's wet dream.
That fanboy is not hypothetical. His name was Marv Wolfman. He felt frustrated by the amount of superheroes in his superhero comics. Specifically, that there weren't more of them. Books like Justice League of America featured seven DC Comics characters which, for the time, was so many underpants in one place that it technically violated the comics code. But Wolfman wasn't satisfied, so he made up a story where all the DC heroes fought a character called "the Librarian," who spied on superheroes from a satellite and sold their information to the highest bidder. So he not only predicted the future of comics, but also invented the NSA.
The TSA was an older DC invention.
When Wolfman broke into the comics industry and proposed these ideas, they weren't well-received at first. However, by 1985 DC was looking for a special way to celebrate their 50th anniversary and Wolfman (who had become a hot writer) had just the thing. He changed the Librarian's name to the Monitor and made him a good guy, but other than that it was the same guy: He still lived in a satellite, still served as an excuse to get all the superheroes together, and still had voyeuristic tendencies.
"I have seen all your penises."