Blocking someone means, "I want nothing to do with this person," so it makes sense that you'll be unable to see what they do. This should include direct messages, threads, comments, etc. @PugJesus's idea of a setting to hide votes from blocked users is a great idea, as you should be able to fully ignore someone you've blocked.
It also makes sense that someone you've blocked wouldn't be able to do any 1-on-1 interaction with you. If you've blocked somebody because they're spamming or harassing you, it wouldn't be great for them to be able to DM you.
However, preventing them from voting on your posts is something different entirely, as votes don't just concern the creator of the post and the person doing the voting; they also concern everyone who sees the post. Upvoting a comment is a message not just to the creator but also to everyone else that you like that comment, and the same goes for downvoting. Blocking voting is much more farther reaching than blocking DMs, and with votes being visible on the fediverse, it's a great way for trolls to hide people's views on their posts.