Primarily, I think the reason voting is excluded is the purpose of the queue is not about post quality or technical merit, but fitness for the site, which does not require voting.
But from your comment on Sam I Am's post:
I get what you're saying, but just because upvoting isn't necessary doesn't mean that we shouldn't have it readily available, IMO. So long as it didn't lead to confusion or cluttering or in some way lowering the quality of reviews, I don't see why it shouldn't be there. I don't know.
I think you are missing something though. By including voting, it might cause unintended side effects. The problem as I see it, is that you are giving an unfair advantage to short (but good) posts that get trapped by the filter as you are going to get more eyes on it. So someone could theoretically get more upvotes for just posting something that ends up in the filter than another user who writes a better answer for the same question. By making you click through to upvote, you can at least survey ALL answers on a question and evaluate them fairly.
You could probably make the same argument for the other review queues as well, and while I can see that side of the argument, I think there are subtitle differences:
First Posts - generally a single user is only going to be in the first posts queue once and it only takes 1 positive review to kick it out of the queue so you won't have too many extra eyes on it. Additionally the whole purpose of the First Posts queue is to judge quality and technical merit, and upvotes (and downvotes) are how we do that here
Late Answers - Just like First Posts, the whole purpose of the queue is to judge quality and technical merit. And since the post is on an old question, it could probably need the extra views to give it a fair chance.