Chinese customers continue to buy large quantities of European and Japanese infant formula while traveling abroad. This is most closely linked to the lingering distrust of the domestic industry following the melamine scandal of 2008 which reportedly affected upwards of 300,000 infants.
The result of Chinese demand in other countries is empty shelves and upset customers. That is the reason you see signs like this one (Japan) limiting purchases to 8 per person. Similar signs can be seen in European countries.
In a typical example of Japanese insensitivity, the notifications are only given in English and Chinese.