Well, in Japan, virtually every bicycle, even the kids ones, has a light on it, so the market is a lot larger, lots more products there. Then on top of that, the product liability situation is a lot more dire in the U.S., so for lots of vendors, the relatively small number of sales isn't worth the hassle of product liability insurance, U.S. product safety regs, etc.

This isn't speculation, I know this for a fact having worked w/some others trying to import some similar stuff a few years back. A lot of these Japanese domestic market cycling products, they won't let their online retailers sell/ship to the U.S. either for the same reason.