Perhaps our government is further hoping to keep the embarassment of this Łucked up and ill advised campaign to a minimum.
Perhaps they hope that the public will forget, if they don't have to see the uniforms at airports to remind them, that our personnel are still being sent into harm's way?
Perhaps they are further hoping that a terrorist organisation is stupid and will fail to realise that our personnel travel are obliged to travel civvy air if they aren't actually seen wearing uniform?
SNAFU.