Why does Vitamin D supplementation have to be conclusive for people to see it can be beneficial on a personal basis? Majority of science is tentative/inconclusi

Why does Vitamin D supplementation have to be conclusive for people to see it can be beneficial on a personal basis? Majority of science is tentative/inconclusive by nature. Medicine is moving to become more personal and preventive rather than purely guess and scientific method driven, especially with the advancement of AI and modern medicine. When I read this trial, I see good news for those who personally believe in Vitamin D and have experienced benefits from it. I see no news for those who do not care for Vitamin D and have not tried it. This is an incremental study that helps push Vitamin D forward in my opinion, even if the findings are weak.