Miasma theory [1], as you are referencing, was not "obvious advice" - it was the scientific consensus, worldwide, for thousands of years in terms of the propagation of illness. Germ theories had been suggested by numerous people for many centuries, but a problem is that miasma theory was deeply entrenched as the consensus view and could also explain most things such as people who are around sick people also getting sick. It's a theory that was extremely difficult to falsify until it became undeniably wrong once we developed the technology to actually be able to literally see bacteria.

On top of scientific inertia, another issue is that "actual, careful study" often fails to detect things that are really there. A great example of this is scurvy. Scurvy at one time was one of the most virulent diseases there was. It killed many millions of people during the age of sail alone and long-term voyages simply accepted the reality that they would likely lose a significant portion of their crew to scurvy. [2]

We now know that scurvy is simply caused by a lack of vitamin C, but one problem with resolving the scurvy mystery over time is that the actual cure sounds absurdly hokey and superstitious. Oh you're dying from this absolutely awful disease that's causing your entire body to deteriorate and rot from the inside out? Here, suck on some limes - it'll cure you! And scientific trials to test the "lemon theory" (which had been written about for hundreds of years) failed to show any meaningful success. The reason is that exposing lime juice to light, air, and certain metals used in storage/delivery (all as happened during experimentation) worked to greatly reduce its vitamin c content.

It was also confounded by the fact that fresh meat also has lots of vitamin C. So you notice claims that fresh fruits seem to cure scurvy and fresh meats also seem to cure scurvy. This now led to the scientific view that the problem was caused by tainted food. So forth and so on, stumbling very awkwardly along again until we reached an era of technology where we could isolate and measure 'vitamin C' and finally prove, once and for all, it was indeed the root cause. As a fun aside, vitamin C was not initially named ascorbic acid. It was named hexuronic acid. It was renamed to antiscorbutic (against scurvy) acid, shortened to ascorbic, once it's effect was proven once and for all. This is also where the slang of a limey for a British sailor came from. They were one of the first nations to require a regular dosing of lime for their sailors.

So there's always a balance in life. It's important for the evolution of our entire species that not everybody believe the exact same thing. Common sense is usually right, but sometimes it's very wrong. And science is usually right, but sometimes it's very wrong. People diverging from the norm to pursue their own views and values is something that benefits everybody as they work as completely volunteer guinea pigs. And it's often the case both that common sense ends up complimenting science, as well as science complimenting common sense.

[1] - https://en.wikipedia.org/wiki/Miasma_theory

[2] - https://en.wikipedia.org/wiki/Scurvy#History