Because it does not need to be changed at the current time.
This is simply a knee-jerk reaction for two reasons:
First and foremost, Blizzard hates the fact that the vast majority of people are using KjC. It takes away from the entire design approach of this expansion. The concept (which failed) that each talent choice would be just as strong as the next; there would no longer be any cookie-cutter specs or preferred talents. People pick KjC for a few reasons and they revolve around enjoying the play-style/gameplay and disliking the other choices in the tier (especially AV which is seen as horridly useless and bad design). MF is a great choice but if you are not in a guild that is pushing 13/13H then the fun factor and gameplay changes that KjC bring can and do outweigh the benefit of MF.
The second is due in part to the complainers who dislike the fact that Warlocks get such a vast gameplay change that they cannot have. It stands out as a waving red flag, in much the same way as Chaos Bolt did pre-nerf. People whole hardly ignored many other abilities that were just as overpowered. Nothing else literally screamed across their screen such as the green bolt flying in for a critical. Oddly enough with the resilience changes and the change to PvP Power CB now hits like a wet noodle. Are they going to revert the change to CB? No. Why not? After all the purpose of the nerf was do to the supposed 'insane burst'.