That might happen sometimes if you add a reply to the old theme version page notifying the previous reviewer that an update has been uploaded. Otherwise, they won't get any notification. Still, this depends on the reviewer and their availability.<br>
<br>This is all volunteer-based in people's free time. It'll fluctuate sometimes. I've learned that if I upload a new theme update, you just have to wait. Whether that's 1 day or 1 month.<br>