Youre over-generalizing. Japan has a very diverse climate, from subtropical in the south to New-England like winters in the north. Also, the Japanese Shinkansen stops for typhoons, but not wind or rain. For snow you're talking about delays, not stops. Just as long as it takes to clear thr tracks. There's a difference. And while parts of the Great Plains have extreme weather, they also have excellent weather systems already as a result. I don't think there's real need to blame the weather for not developing to system. And it's not always necessary to go at top speed to be fast enough.
(I happen to have lived in Oklahoma for ten years and Japan for twelve).