They bred up a mouse that gets something that looks like Alzheimer's, and is very easy to cure it in. In the US, most of two billion dollars annually goes for grants just to study this mouse. Vanishingly few grantees ever so much as peek at anything in or from human patients. Of course there is plenty still to learn about that mouse, as about any organism, but what has been far more thoroughly demonstrated than most medical results is that, appearances aside, Alzheimer's in that mouse is very unlike in humans.

The only intervention I know of that shows robust results preventing Alzheimers is having been recently vaccinated. It doesn't seem to matter much for what, but several population studies, involving tens of thousands of patients and controlling for lifestyle confounders, show a reliable 40% reduction in dementia risk for people recently vaccinated for TDaP. Nobody will talk about it, apparently because it is embarrassing to have no clue why it works. (Pressed, people mumble about inflammation.) And, of course, no money is spent figuring it out, or figuring out why vaccination doesn't seem to help the other 60%.

Work in other countries has implicated herpes virus, and got good outcomes from valacyclovir, again provoking little interest from US researchers.

Whenever it, somehow, becomes possible to divert those two billion dollars to somewhere they might do some good for Alzheimer's patients, a whole population of biochemists who only know about brain metabolism in that mouse will need to find something else to do. In the meantime, they get to allocate the money to themselves.