Hear me out for a second 
Imagine Trump's DoJ's inserts some outrageous allegations that nobody would believe in the first place, and then says "look at how HONEST and TRANSPARENT we are, we're even releasing these submissions to the FBI!". Leaving out that these are accusations like "Trump and Epstein are ALIENS!".
Or if they're not made up entirely, perhaps they've cherry-picked a handful of the most not-believable accusations?
Easy to see IMHO why doing something like that would have value towards convincing the public that they've released everything, without actually doing anything remotely like that. And by highlighting (or even fabricating) particular, sketchy "submissions", they could be attempting to create a sense that ALL accusations against Trump are similarly ridiculous.
I guess it comes down to: What is it they included in the 30K documents? How credible is any of it? If it's mostly or entirely not credible in the first place, then I think I've sussed what's going on 
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