I can't remember if it's in this article (read it in the magazine last month so my memory is foggy) or another profile on him but it said he wasn't overly popular in Japan as he's going against conventional wisdom and overall tradition. I don't know enough about the whole sociology of Japanese people and business to say whether that's accurate but he does seem to draw a lot of ire over the way he's gone about things.

Check out this Financial Times piece on Hiroshi Mikitani. It talks quite a bit about ‘Englishisation’ and the contempt felt against Rakuten.