I think its the fact that you can miss with pretty high chances with the white attacks, at least thats why im not using fury for pvp. You cant really stick to an enemy in pvp and its to much penalty for you to miss damage if you are not cc'd. The other thing is that Bloodthirst has nearly no damage against players with high resilience (on the other side mortal strike at least has some damage advantage against bloodthirst). One more thing can be the colossus smash reset, it is really high damage increase in pvp. At least thats my POV. I hope i have answered your question at least. i have tried!
You see Arms in PvP because burst is important in PvP and while Fury has great burst it's random. Arms can line up burst damage on a schedule where Fury has to line up enrage which is proc based (i.e. random). Also Fury has a much higher miss rate than Arms so rage generation can also be an issue.