re: Sycamore Bench

Duck when all one ever knew from birth on, when all one ever saw, when all the tools ever shown was/is Imperial why would one ever seek a measure that was completely unknown, not available and totally foreign?    
Some of my tapes and sticks do have metric on one side but why go to the expense and trouble to replace perfectly good, known, and reliable tools with something that is unknown.
It would be a lot of confusion to.make a project that was to be used with items of imperial sizes in metric.   Too much trouble.
Believe it or not in maybe the 8th grade in school we did get exposure to metric as well as the abacus and other things. 
At my age, 86 my mind has had years of conditioning to thinking inches, eights, etc.  To clutter up what is left of those grey cells with millimeters, centimeters, kilos, and such would be or could be disastrous, my projects would have kilos of errors for sure.   So 2 inches by 5 1/4 inches it is.  
Besides I have no idea why 5 1/4 was used.