Because the bourgeoisie that lead the French Revolution famously remained 100% in lockstep with the underclasses. There was never a moment where the needs of the rulers diverged from the needs of the masses and a whole new regime of class strife arose from it, no sir.
The metric system was applied top-down to french society by its ruling class, it was not some grassroots attempt to make the world better.
read the xkcd comic
There’s nothing quite as intuitive as a table of numbers and associations that you can memorize by rote. Pass me my flash cards!