That's because Tolkien was logical, and had no use for things that didn't make sense. Which is why I love his works.
And, FYI, France instituted a convoluted calendar that consisted of 100 minute hours, 100 second minutes, and something else that has escaped my logical thinking. One hundred hour work-weeks?
*sheesh* I'm thinking it's way past my bedtime.
Don't worry yourself into a tizzy over it. You are trying to apply logical thinking to France, after all..