They already factored in some amount of tariffs into the US price. It's not really that it's cheaper in Japan, but rather it's more expensive in the USA. It's also US$65 cheaper in Australia, for example, and even cheaper in the UK.

(keep in mind that advertised prices in Australia and the UK include tax, so you need to subtract the tax to compare with US prices)

The tariffs are just a lot higher than everyone expected. Nintendo were probably preparing for a 20% tariff, not a 54% one.