Well, to put things in perspective, WK has 9087 items in it. 2000 reviews is fully 22% of the content on the entire site. If many of those items have been completely forgotten, then that would be like trying to learn literally hundreds of words/kanji all at once (compared to learning them the normal way through the levels, where the lessons become available to you gradually, forcing you to stagger them).
The way the SRS is set up, it’s designed around the assumption that you will be able to clear out your reviews and get them down to zero on a constant basis. The first two apprentice stages come back 4 hours later and then 8 hours later. If you have a huge pile of reviews, it’s unlikely that you’ll be able to get to those reviews in time. The longer you wait on them, the worse your accuracy will get. If you fail a higher level review, it goes back to guru. Fail a guru review, it goes back to apprentice. (For an illustration of why accuracy matters so much in terms of reducing your overall workload, see this simulation).
For most people, the apprentice items make up the majority of their daily review churn. For people working through a huge backlog, they’ll gain more and more guru and then apprentice reviews as they fail reviews on the master and enlightened items, which adds more and more clutter to the pile. Without having a way to sort through the pile so that you can knock out those lower level apprentice reviews when they come due, you’ll be at a severe disadvantage, and you could literally do reviews every day and still see zero progress in terms of overall numbers.
Which is why many people recommend using a reorder script to reorder your reviews so that lower SRS levels float to the top so that you can get those done, first, and push them up to higher levels. If you do this, you might have hundreds upon hundreds of enlightened items that you don’t even see for weeks because they’re basically locked out by the script until you’ve cleared out the lower level stuff.
Essentially, this recreates the vanilla WK system by artificially limiting the amount of items you’re reviewing at one time, so that you have time to properly learn that set of information before adding new stuff. Trying to learn too much at once means you can’t effectively practice everything, which means it’s a lot harder to properly learn it, and you need to spend more time with it, which is vastly less efficient in the long run.
Also, if someone doesn’t study at all for a year, pretty much all of your existing apprentice reviews have been completely forgotten, and the guru reviews, too. Probably many of the master level items as well, since it has been a lot longer than a month since you’ve seen those items. Even the enlightened items will probably be tricky, because a year is a lot longer than four months. Many people in that situation would be better off just relearning from scratch all the levels where all items are at master and below (at bare minimum). If you have to relearn it anyway, might as well do it through the gated level system instead of trying to do it with zero gates (using vanilla review order), or trying to recreate the gates (using a reorder script).
For an example of how a review pile can actually take you longer to get through than resetting, one user has been trying to get through a pile that is thousands upon thousands of reviews. This user reset to level 47 (from 60) in June 2021, and had 5288 reviews. Cross-referencing with my own study log, I was level 11 at the time. Over the year and a half or so since then, that user is still level 47, and I have made it to level 51.
So I have actually managed to outpace them by four levels, despite being so behind when they started working through their review pile, and I’ll likely achieve level 60 well before they reach it again (assuming I don’t fall off the wagon myself, haha). Obviously, the pace of the individual factors into this a lot, and I do in fact do more reviews daily than that user, but I’m by no means a speedrunner! Review piles are just really, really hard to work through, and it can be incredibly demoralizing to do so.
For the record, I’ve never had a review backlog myself, but I’ve read many, many accounts of others on this forum trying to get through a large review pile, and that has been enough to scare me into never wanting to go through that experience 
.