I think I need to explain this, a little bit better.
The Wii U shortages, as far as I can tell, are (or better said, were) caused by an internal production problem in Mitsumi Electronics Co. This company was one of the manufacturers of the Wii controller and some parts of Wi-Fi PCB for DS, in the Wii/DS era, and now is dedicated to manufacture some parts for the Wii U hardware.
Their factories are located (at least, those focused on manufacturing Wii U) in China. The Wii U stock problems started somewhere around the beginning of the festivity of the Chinese New Year on February 8th (new moon), and they stopped the production. This festival ended on February 22nd (full moon), that's why
Rakuten and other blogs expected that Wii U shortages would have ended by around that time (late February to early March), since there are not factories in Japan and there are some difficulties to send the production from China to Japan.
What is the problem, now, that there is no reason for shortages? Well, doing some research, I found that Mitsumi Co. became a subsidiary of Minebea (another electronic company) and announced an official integration with this company.
http://shikiho.jp/tk/news/articles/0/97891
http://eetimes.jp/ee/articles/1512/22/news046.html
In early February, they had to revise their expectations to explicitly declare a six billion yen deficit on their anual report.
http://www.nikkei.com/markets/kigyo/gyoseki.aspx?g=DGXLZO9693979004022016DTC000
http://www.fukeiki.com/2016/02/mitsumi-2016-loss2.html
http://m.finance.yahoo.co.jp/news/detail/20160204-00000226-stkms-stocks
http://shikiho.jp/tk/stock/info/6767 (with some graphics)