Presumably, because the more prestigious journals declined to publish it.
Why did all of them decline to publish it? There was probably a reason. Papers published in a quack journal does actually carry a signal about the quality of paper, IMO. No one turns down publishing in Cell or Neuron to publish in Donald's Journal o' Quackery and Crockpot Recipes.
Now most quack research is not particularly useful… but it can be made more useful to society if it’s used properly, we should be more willing to publish reproductions and failures to reproduce existing research, and we should be encouraging early career scientists in all disciplines to take this kind of quack research and to prove it wrong, it’s all there to disprove, easy done. We would get more critical thinking in our research students we would get more evidence to disprove other quack research and every now and then we might even stumble onto something good that would have gone ignored as just quackery for an unknown period of time.
If we want to fix the reproduction crisis we can’t ignore the shit research papers and only reproduce the good ones we think might work, we need to be willing to look at research like this, which invoices a pretty/relatively harmless high dose vitamin regimen that can be easily monitored by a clinician performing the research work (double blinds of course) and then we go from “idea that won’t be touched again and quacks try to convince people with flimsy research” to “idea conclusively proven or disproven and scientifically have settled the question without leaving reasonable doubts that can be used by quackery peddlers or others mis-using the scientific method for their own gain.
There’s a reproducibility crisis in many fields of research, and medical research has multiple confounding factors, the “no prestige in just redoing the research”, lack of money for trying things that might fail to generate RoI for pharmaceutical companies, and the general medical research problems of clinical trails and ethics review and all the other stuff involved in good quality medical research.
Consequently this stuff gets thrown in the quackery bucket and ignored. It’s frustrating to see things that won’t hurt anyone to try again and properly debunk or expand the evidence for, winding up in an ideological trench war where the outcome is getting to enter round two of the “funding your actual research” trench war.