> If this study was reproducible (it is not) someone would have started using it

That supposes that there is an army of researchers dedicated to repeating expensive experiments. As far as I can tell this is doesn't exist. Especially in cases like this when it's obvious that the experimental protocol lacked controls and hence would cost more to repeat than the original study.

There are plenty of things that are not reproducible yet they make their way into text books and general practice.

I don't know if the claims in this article are correct but it is suggestive nonetheless:

"The analysis, which is published in the Journal of Clinical Epidemiology, included 154 Cochrane systematic reviews published between 2015 and 2019. Only 15 (9.9 percent) had high-quality evidence according to the gold-standard method for determining whether they provide high or low-quality evidence, called GRADE (grading of recommendations, assessment, development and evaluation).

Among these, only two had statistically significant results – meaning that the results were unlikely to have arisen due to random error – and were believed by the review authors to be useful in clinical practice.

Using the same system, 37 percent had moderate, 31 percent had low, and 22 percent had very low-quality evidence."

https://www.sciencealert.com/around-90-percent-of-your-medic...