Some companies when they have overstocks or un unsold items out of fashion or out of the scheduled time life run sell these items "by the weight" to international merchants with the sole condition to be sold in a country "out of his market". That´s why you can find these CDs in China, by example.

This is not only about Japanese Mini LPs. I will show you an example from my country (Spain):
http://www.discogs.com/sell/list?release_id=2988430&ev=rb

There you will see 4 CD units of the album "Koniec" from the spanish band "Chucho". 3 of them are being sold from China starting at $3.00
(about €2.21) and the 4th is being sold from Spain at €17.19. It´s more, the 3 units from China are Still Sealed. Are they original? Yes, I can proof that, I have one unit bought in my country and another one bought from that dealer in China.

In this case, the spanish label -Sinnamon Records- went out of businnes in 2008 or 2009 and from that day no more products left his warehouse. Probably all his stock was put on auction by the court to partially pay his debts.

So here have 2 of the common situations: get ride out of overstocks or bankruptcy. Japanese Mini LPs are in the first case (overstocks).

Hope this will answer you.

Txomin