"Tatemae" (facade) reasons are that he called the area immediately surrounding the broken nuke plant "a ghost town", and that he tried to rub radioactive materials on his protective clothes against reporters who are the members of the official press club.
And a big chorus of "Oh he hurt the feeling of people in Fukushima! Poor victims!" was orchestrated.
(What else would you call a deserted town around the nuke plant, other than "a ghost town"?)
Many in the independent and alternative media don't think they are the "hon-ne" (real) reasons. They believe his stance on nuclear power plants (he wanted to phase out) and his plan for radical restructure of the Ministry of Economy, Trade and Industry (he wanted to remove certain pro-nuke officials), and his reservation about TPP (Trans-Pacific Partnership, a pan-Asian free-trade scheme promoted by the United States).
Mainstream media reporters couldn't even agree on what exactly the minister said about contaminating the reporters with radioactive materials, which led many to believe this was one of those crafted stories to put up as a facade for taking down a person that they and their friends in the government do not want.