whoever created YoRHa. The entire purpose of YoRHa was to perpetuate the human lie, and then perish so that the war never ended. They were sacrifices to the continuation of the war. Hence the machine core AI systems, as their creators didnt feel comfortable creating their sacrifices with actual android AI cores. Pricks.
Actually not quite, YoRHa were never originally supposed to be martyrs dying to keep a lie preserved. they were originally just a group of advanced androids brainchild of a single Android named Zinnia who would fight for mankind and give false hope to the others. When the Prototype of 9S: No.9, found out his creator had constructed him and No.2 (and the rest) from Machine Cores and that they were only here to spread a lie he went berserk, killed him and went on to add the backdoor and disposal idea to Yorha to make the lie even harder to uncover before getting killed by Number 2.
You can also see the Voice Actors of 2B and 9S act this out on his twitch stream here