Any Idea Why JDM/USDM Plug Wires Differ?

Okay, while I was tearing down my new JDM motor to get to the ceramic turbo, I noticed that the JDM Spark plug wires look like about 7 or 7.5 mm as opposed to the USDM Plug wires that are about 5 or 5.5 mm. Now, I don't see any specific reason for this, especially because the JDM TRD Plug Wires that I had my friend buy last year for me are the same size as the USDM wires. I know that Size doesn't matter with these things, but I still wonder why the JDM ones are better insulated.

Any Ideas?

Are you sure that wires from your JDM engine are stock?

They look really stock to me. The great dirty black color with the basic black connectors on either side. There's no way I can tell for sure if they are stock, and also any writing that was ever on the wires is no longer. I'll post a pic whenever the site starts working again.

its not JDM VS USDM, its from the years,
90 and 91 i think they are the same, 92 -95 different. i noticed that when changing my 90 engine for my 92RC engine

Yup. The 90-91 had the nice fat wires and the 92-93 (or -95 if we include USDM MR2s) had the skinny. If you order TRD wires they are the same thickness for both "versions"