First thing I thought about was the reasoning behind why Tor uses Entry Guards (a limited set of relays chosen by your client to use as the first entry point rather than a random one each time). I'd imagine the same arguments apply for why you don't want to randomize which servers your DNS queries go to. If you're making hundreds or thousands of queries, as people tend to do while using the same set of sites over time, then eventually all servers will end up with the names of all the sites you visit, as opposed to just choosing one server and only that server having the names. So yeah, that definitely seems like the opposite of a privacy feature.

More info on why Tor chooses just a few entry nodes here: https://support.torproject.org/about/entry-guards/