Those who championed the amyloid hypothesis truly believed it, and thought that focusing money and attention on it rather than competing ideas was the surest way to an effective drug.
Or maybe the real problem is the excess emphasis on finding a drug in specific that can be commercially monetized. A single drug for a single cause of what is likely a complex process.
Amyloid and another protein (tau) accumulate in the brain due to sleep deprivation. Helping people get a good night's sleep -- without drugs -- would likely help, if only to stave it off in those at risk.
The problem is it won't create any razzle dazzle "unicorn" companies and newly-minted zillionaires.
One of the researchers in the article found that herpes simplex infection promotes the accumulation of amyloid. Her research was not irrelevant to the amyloid hypothesis. It was only irrelevant to an agenda to find a drug to treat amyloid.