What exactly would firing him accomplish? Further diminish investor faith in Sony? Have any suggestions on who should replace him? Kutaragi perhaps? A pointless endeavor. How would it improve Sony's sitatution?
A huge misconception about Sony is that CEO Kaz Hirai calls all the shots. However, he only calls some of the shots because there is this thing call "executive boards". Kaz may have a really good vision for Sony, but his vision could be held back by the executive board that has other ideas. This is why firing Kutaragi and the stepping down of Howard Stringer didn't help Sony that much, because they are only a few of a potentially large number of people that are holding the company back.