“Why does it need to be unanimous?”
Because otherwise we have no way of knowing definitively that it is true. Amid great trepidation I would go a step further and say that my answer has to be right because since you can’t prove definitively your idea about H’ forcing the psak to reflect the truth, that means that there is always a possibility that my answer is right and therefore there is a possibility that anything (that there is a machlokes on) is incorrect and therefore it becomes impossible to have emuna sheleima in any disputed matter.