Did we ever figure out why 15% was the magically common layoff number over the past 18 months or so? By "figure out", I mean something beyond mere conjecture.

Did we ever figure out why 15% was the magically common layoff number over the past 18 months or so? By "figure out", I mean something beyond mere conjecture. (Sorry for the tangent. I just thought of it because I noticed this layoff is something other than 15%.)