Your question contains the answer. They dont want tanks and vigilance to use it, thats why its bound to shi-choo now.
Although i feel they didnt looked into all changes this will do.
On sentinel they couldnt switch, altough they wanted to implement free force scream, so they moved it into pve bonus. I bet they forgot about pvp players who cant get the bonus. I bet they also forget about guardians who may obtain this 2 set boni, creating an incredible strong synergy for masterstrike.
I can maybe see focus guardians opting to go for the pve 2pc set for the blade storm bonus, but vigilance guardians are definitely going to stay with the 4pc pvp bonus.