It even makes a bit of sense that they're terrible spies?? The training to make them assassins is heavily implied to be torture, like, you cant do that to a bunch of people if you're going to leave them without supervision/supervised by someone way weaker than them AND also give them training to ferret out secrets. What if they started to spy on the wrong people?? It's also inline with the brute force approach the World Gov uses for everything else.
YEAH...there’s this fine line the wg want. they want to uncover other people’s secrets, but they also want to keep all their secrets (and they have a lot of them). so training people to figure things out is dangerous for them. especially when they want absolute loyalty and do not tolerate dissent in any form.
and in the end, that brute force method works. cuz cp9 do get the blueprints, and nico robin, and very nearly succeed in what they wanted to do. but they do it through interrogation, threatening, and kidnapping (i.e. force), not any kind of espionage.
it really gives a sense of how the world government works, and how they hold power and control over the world, despite having terrible bureaucracy and internal affairs.