Because moderators and 2K+ users have enough to deal with already. 

It's not a good feeling coming on to the site and then seeing 70 or so edits in the queue that *all* need to have both versions read, evaluated, managed, and acted upon. Such a queue can potentially take *hours* to sort through if there was no sanity limits. Also, because of the double-review feature (it takes two 2k+ users to approve an edit), it could take even *longer* to go through the queues. Not to mention the fact that we can only review 20 suggested edits a day.

Additionally, edit queues also bring trouble posts to our attention. We get a chance to review the post itself to notice trends with users. We can see trouble users on both sides of the queue. We can see if tags are being used or misused. We can then act on all of these problems accordingly.

Additionally, as pointed out by Terdon, users get +2 reputation for editing posts under the 2000 rep mark. This limitation allows us to throttle users attempting to grab a lot of rep very quickly, especially with insignificant edits. If this limit weren't in place, someone could theoretically write a spell-check bot and spam the review queue and potentially reach 2k in one day (that is, if the reviewers are feeling nice).

We focus on ***quality over quantity.*** If we allow users to make 150 pointless edits in a period of 15 minutes, the queue would be already more annoying and harder to work with than it already is.