Most people are going to be uninformed about medical science. (Hell, most medical practitioners struggle to stay informed). Worse, there is a strong bias towards misinformation--look at the health supplement market, which is basically a market the seedy snake oil sellers set up to get around FDA regulation.
On top of this, keep in mind that it is very easy to accidentally design bad experiment methodology. With respect to clinical trials, it's all too easy to take a failed trial and say "it actually worked on this subgroup" because there are often enough subgroups to find one with a spurious correlation. And when you have monetary pressure to salvage a failed product, the p-hacking is less likely to be internally questioned. The current regulatory regime requires that you declare how you're going to define acceptance before you run the trial to prevent this kind of p-hacking, and if you truly believe that you're not p-hacking, you're welcome to submit another trial to show correlation on that subgroup (unsurprisingly, many of these end up coming negative).