You can find more information about how Stack Exchange works on the site dedicated to exactly that purpose. When you come across a situation that isn't immediately straightforward such as this, it's best to check on Meta Stack Exchange first. You'll often find perspectives on the function/mechanism fits into the broader Stack Exchange system as well, and why it works in that particular way.
In particular, this question and its answers give most of the basic details.
[I]f enough people (currently 3) select "Leave Open" within the review queue, the question will be immediately removed from the queue (not shown to any more reviewers) and the aging starts immediately.
This doesn't prevent it from being closed, mind you - if someone visits the question directly and votes to close it, that'll both count toward the 5 votes needed to close it and stall the aging for another four days (14 days if it has less than 100 views) - but it will both reduce the number of people viewing it and hasten the removal of votes on questions for which there is clearly no support for closing.
That is, a Leave Open review result will
remove the question from the Close Review Queue,
immediately begin aging-away the existing closevotes,
Note that the threshold for removal from the queue is to meet either three Leave Open votes or a moderator choosing Leave Open.
Other people have suggested the same thing as you and there are good reasons why a Leave Open vote should not cancel a closevote.
It comes down to the fact that Stack Exchange wants increasing quality, not quantity. It's better to have a question improved before the answers come in, to prevent the answers from being wild guesses, generically vague, or a list of all possible solutions for any situation (instead of specific answers that respond directly regarding a particular situation).
The result is a system that errs on the side of caution. If a question gets closed a little prematurely, and receives improvement while it waits for reopening, it will waste a lot less effort than leaving open a question longer than it should have.