Exactly as we're told on forums, exactly as we're told on TV. This is how you know Epstein is also innocent and why it won't be investigated, because we know people cannot keep silent about committing crimes, therefore we know no crimes were committed.
That's both a good point and not so much. In the end, they didn't keep their mouths shut, Snowden spilled the beans and uncovered the large conspiracy. It's a good point with regard to "that would require a large conspiracy, and those don't work" not being a good argument against theories: there might be a large conspiracy that just hasn't failed yet.
And who knows how many more years or decades the large conspiracy would have worked just fine if Snowden hadn't leaked.
And yes, conspiracy theorists don't have an accurate appreciation of how hard it is to manage projects and keep them secret.
There are plenty of conspiracies, plenty of which have become known. The point is that there is a limit to the number of participants, significance and age of those that are not yet known.