It doesn't have to be like that, but what form of a standard do you have in mind.
How about the width of the hand,,,say you are 15 hands tall.
Using a tank of waster with a pin hole to tell time,,,well it is 6 liters past noon.
It works, it is just something accepted long ago as being a standard, something everyone agrees on. Just not globally as in the SAE standard, your meter is near our yard. Our mile is 1,609 of your kilometers.
The scientific community has much adopted the metric system as standard, it is a good system.
It is convenient working with base 10 numbers, going from kilometer down to micrometer,
Taking a mile down to an inch takes a more complicated math, numbers other than 10.