I might be wrong but I feel like WBR treats variation (looking at the measure and saying "it has changed") as a trigger point for investigation rather than conclusion.
In that case, lets say you do something silly and measure lines of code committed. Lets also say you told everyone and it will factor into a perforance review and the company is know for stack ranking.
You introduce the LOC measure. All employees watch it like a hawk. While working they add useless blocks of code an so on.
LOC commited goes up and looks significant on XMR.
Option 1: grab champagne, pay exec bonus, congratulate yourself.
Option 2: investigate
Option 2 is better of course. But it is such a mindset shift. Option 2 lets you see if goodhart happened or not. It lets you actually learn.