Trivial? It might seem so, but it does actually fall well within the area the founders gave congress (surely this is both weights and measurements and interstate commerce).
"Fixing" the standard size would be fraud, as they don't sell the actual product that they claim to sell.
Would you mandate your system or sizing? What if they just changed their form of measurement? Or they said recommended size? Is this a problem you are constantly facing? I don't have any difficulty buying pants - why do we need a law?
"Fixing" the standard size would be fraud, as they don't sell the actual product that they claim to sell.