Language popularity can make a significant difference. Using DDG for purescript queries gives iffy results often enough that I instinctually add the g!. However, for something like Java, or even Clojure, I find that the top result across both engines is more or less the same

Maybe it's because Google keeps your previous queries and knows more about what you're looking for unless you wipe previous searches, whereas duckduckgo doesn't do that. It just gives you the standard results resulting in a bimodal results curve. For some people those are perhaps better than a concerted AI attempt from Google. Just a hypothesis though, no proof.