There was no theoretical reason that washing your hands would do anything to combat the spread of disease and all the smart doctors knew otherwise. Some kooky doctor named Semmelweisz proposed that doctors should wash their hands between childbirths in 1847, 14 years before Pasteur published his findings on germ theory in 1861. When some doctors listened to him maternal mortality dropped from 18% to 2%.
I'm all for basic science when the statistical significance becomes so great it really starts to look like causality and then you start figuring stuff out.
It doesn't seem like the statistical significance of the amyloid theory is strong enough that the direction of the arrow of causality can be determined. That's too bad.
The strength of the effect of keto diet interventions in Alzheimer's is pretty strong to my understanding. Which should be aggressively hinting that there's likely some as-yet unknown causality that's worth investigating. We don't have to spend billions to do that. But we do need more funding for it which is hard to get while all the amyloid hypothesis folks are really invested and clamoring.