Really!? Why that there is no attach rate over 100% in Japan also!?

Because, Japan is... unique.

I'll never understand why people buy something twice, one to use and one to collect. To me it's silly.and, most of the time, a waste of money.

Oh, well. This time it has helped Nintendo achieve an extraordinary feat.

Reality is that Japan is not strongest market for Zelda while US is.

That's not even the main thing I was referring too (though it is one reason).
I mean, 1-2 Switch has been holding steady and actually been selling decent over there.

They're quite the odd culture, those Japanese.

Ka-pi96 said: eh, it's not really that crazy. Just look at the rest of the launch lineup and it's pretty obvious why Zelda has such a high attach rate

How dare you diss 1-2 Switch!

And they say there's no such thing as a "Killer app" anymore.

That's a pretty good attach ratio..

So there is apparently 21,000 people who get their jollies buying multiple copies of Zelda...?
Or... less people than that are buying even more than 2 copies... Japan's got competition for weird.

Seriously, is that some sort of carry trade, to countries where it hasn't launched yet? or side-channel exports are cheaper?

21,000 people are buying Zelda not to play it, because they already bought another copy but that's not good enough. 
Who knows, maybe they're buying multiple Switches to go along with the extra Zelda copies.