Voting is one of the main components of SE communities. While surfing or reviewing posts I am eager to vote on them.
Answering is also one of the main components. Flagging's gotten pretty big too. But neither of these are available in the current review queues.
Note that you can't close or vote to delete from the suggested edits queue either, or dispute closing in the LQ queue.
The core philosophy here is that each queue focuses on a specific task or question, and provides the tools most important for resolving it. If you want to do something else, there will always be a prominent link to the full question page.
A concern with allowing voting in the Low Quality queue specifically is that you're not viewing answers in the context of other answers, or a question in the context of its answers. You're never able to vote in these circumstances normally - it's worth remembering that voting directly from the list of questions was considered early on, and discarded as too likely to produce bad results.
Finally I should note that even though I'm declining this, voting might make sense in the future on different types of /review queues. The objections I've outlined above would have to either not apply, or be mitigated in some way though.
Update: voting allowed (and encouraged) in First Posts and Late Answers queues
Based in part on this discussion, we've enabled voting (and most other post-specific actions) in the First Posts and Late Answers queues. The concerns I expressed above
still apply, however:
The importance of guiding new users early, and getting attention for answers that might otherwise be too easily overlooked, is important enough to justify a little bit of extra attention.
The amount of skew enabled by this (both to post score and user reputation) is limited by the posts allowed and the attention granted them: only one post per user (for first posts), only posts from very low-rep users (<= 10 for late posts), and only one "active" review per post before dequeuing.
While I strongly encourage folks to vote in this queue, please use common sense: if you don't understand the subject of the post, just click "Not Sure" and move on.