I suppose that it's possibly driven by a move towards more "sportbike" type scoots, and away from the old 50's Vespa-style ones, which are really considered toys here in the US, and not serious bikes. If only people knew.
I went to the grocery today, bought some stuff, and a bunch of college kids followed me out with their weekend beer. One of them loudly snickered, "oh it's a moped..." So I stopped dead in my tracks, turned and asked "any of you ever heard of a 400cc moped that needed a license plate?" That pretty much shut them up. Immediately followed by stares when I started it up...