Why exactly does glucosamine only having a minor effect on pain, collagen degradation, joint function, etc. preclude it from having an effect on cancer outcomes

Why exactly does glucosamine only having a minor effect on pain, collagen degradation, joint function, etc. preclude it from having an effect on cancer outcomes? Obviously this should be replicated and if not replicable, should be dismissed. But it's perplexing to dismiss it out of hand because its effects weren't strong enough for an array of other totally unrelated health outcomes.