I would imagine there are various reasons behind the decision to limit, one of the most notable ones is from an answer by Jeff Atwood:
We really want vote diversity here, so that's the point of the limits
-- if the same 2 folks are vetting all the edits, that's not a sufficient set of eyeballs on those edits
Also, having a higher daily review cap means you open up the doors to more bad reviews, from robo-reviewers, people just aiming for badges, etc. And even those attempting to do good reviews should perhaps take a break - i.e. 20 reviews in a day is enough for anyone really.
This does of course hinder our getting more reviews done by those users who would carry out good reviews with their additional - but such is the world, the few can spoil it for the many because the negative effect of the few outweighs the benefits of the many.
We all know that moderation is a vital part of SO, I'm very eager to
know any positive spotlight for the above concern.
What concern? Is there a need for users doing more reviews than they can now? Is there a queue with a problem?
Even on Stack Overflow (ignoring close votes) the queues are turned around pretty quickly.
When I see a few hundred reviews in Triage or LQP, 5 or 10 mins later they're all done.