Nowadays, getting reviewers is a challenging task for many pure mathematics journals. How would an editor be able to find a reviewer for a very new theory that nobody has worked on yet?
If the author is a big name in some field, an editor might consider doing the hard work in searching for referees and the referees will also agree to reviewing for them.
If it is from a not-so-popular author on the other hand, it might have a high chance of getting desk rejected. In such cases, how can we expect new theories to be developed with the current system?