Standing on three legs is a genuinely vulnerable thing for a prey animal. He cannot leave, he cannot balance the way he normally would, and a stranger is holding the leg he would need to move first.
None of that is about the farrier, and none of it is about the hoof. Hold harder and he learns that the leg gets trapped, which is the exact conclusion you did not want him to reach. So we build the opposite. First a relaxed starting point and control through the feet on the ground. Then touch, then lifting, then holding, then balance on three legs, each one only when the one before it is genuinely easy. The tools and the noise come last, before a farrier ever needs to be present.