We have to realize that medical doctors are not, as a rule, scientists. They typically get their doctoral degrees without personally ever doing any actual science, beyond pre-cooked experiments in lab classes. Instead, they have read a great deal about what other people who did science said. But what people say is not the same as what they do, and paying attention to what they say is not a substitute for doing what they did.

Instead, doctors are obliged to memorize a great deal of what they are told are facts. Probably most of what they are told really are facts. But there is nothing systematic distinguishing facts with a great deal of support from those that are just repeated lore, like the business about airborne disease transmission.

Doctors have rejected evidence for airborne transmission because it contradicts what they were taught are facts, with no warning about how shaky any asserted fact is.

Another source of resistance is that facts, to be believed, need a theory. A fact without a theoretical mechanism by which it must operate is rejected. We saw that for cholera before germ theory made sense of it.

For a current example, in doi:10.1093/gerona/glab115, it turns out that having had a recent TDAP vaccine (which you can ask for at any pharmacy) turns out to predict, very robustly, a 40% decrease in onset of dementia among patients at an age where they are at risk for it. A 40% effect size is enormous! At this point, nobody knows why. Is it the tetanus, the diphtheria, the pertussis antigens? Or something else mixed in? Nobody knows. But without a demonstrated mechanism, nobody can allow anyone to see them to take it seriously.