AFAIK Alzheimer’s is a single disease, whereas cancer is kind of a catch-all category for a huuuuge set of different disorders caused and treated by different things.

Alzheimer's is currently categorized as a single disease. But I suspect the result will turn out to be similar to Ulcers which were initially thought to be the result of acid diets, and predisposed conditions, but turns out there are many types, and the most common type is bacterial.

I think we'll find there are many types of Alzheimer's, some Amyloid based, others viral, or dietary, etc.

I wanted to argue against this, but the strongest interpretation of what your saying could hold up to reason.

Perhaps there are some kinds of prions, or other, maybe similar, infectious agents, we haven't isolated yet.

I think it's extremely likely it's caused by something either unknown or previously considered to be safe for humans. Would be nice to study groups of people and see their rates of this illness. Multi-group elimination diet, with HTMA and blood and bone marrow tested for presence of metals, oxidants, etc.

I'd like to assume epidemiologists are all over this?

I think the main problem is that there's no money in saving old people. The current system we have is built around what can benefit the pharmaceutical industry the most, on a long-term basis. Old folks die too soon and often don't have much money to begin with, so sadly it's likely not high on the priority list.