There's two problems here.
1. Are those the actual DC's you'd use in a 5e game? Because, if they are, they are very high. A DC 20 check is on the bleeding edge of what an expert could answer with any sort of regularity. IOW, a DC 20 should basically result in the DM handing the player the Monster Manual, or something very close to it.
2. Do you normally not actually take context into account? Telling me a bunch of trivia that has nothing to do with what we're doing right now isn't helping anyone.
Are there actually DM's this oblivious or is this just some sort of Message Board myth? I mean, good grief, we see a troll and the player asks, "What do I know about trolls" and you're going to give them useless information on a successful check? Really? On a failed check, sure, "You don't really know anything, sorry" is perfectly fine. But, on a success?