A hypothetical way to dox someone would be using the extra data available. Maybe they don't comment much about their particular interests, but they upvote stuff in location-specific communities, downvote people expressing a particular ideology, and anything else that would allow a (ridiculously dedicated) bad actor to work our a lot of personal info about them. Unlikely, but theoretically possible.

Also apparently Lemmy votes are marked as private but any software can choose to just ignore that request, which seems pretty open to abuse.