Speculation.

Here's a new quote from NoA:
“Some amiibo were very popular at launch, and it is possible that some amiibo in the United States, Canada and Latin America may not be available right now due to high demand and our efforts to manage shelf space during the launch period. Certain sold-out amiibo may return to these markets at a later stage. We are continually aiming to always have a regular supply of amiibo in the marketplace and there are many waves of amiibo to come.”

It's launch period and people are being played. I expect pre-orders for wave 3 and onwards to be much higher.

EDIT: http://www.gamespot.com/articles/nintendo-issues-statement-on-amiibo-stock-in-ameri/1100-6424126/

but if youre selling limited stock in the first place it doesnt make any difference, if you make and sell 20,000 in ten days or one, its still the entire allocation sold.

and theyre pulling stock that "doesnt sell well", rather than making the stuff actually in demand limited.

its stupid, it doesnt attract high demand at all, it just attracts scalpers, which drive up the cost and make people LESS likely to buy and use them.