The Amyloid hypothesis persisted for so long because we didn't have any obvious counterarguments since it is so hard to do studies on the brain. Which also means that it's not a bad hypothesis.

What happened is we got the tools to start studying viral associations with other diseases and ... whooops ... suddenly there are associations. The shingles and RSV vaccines seem to affect dementia while others like influenza don't.

Now people can ask questions about why those particular vaccines affect dementia while others don't. And suddenly we have falsifiable tests.

Now we can subject all hypotheses (including Amyloid) to stronger scrutiny.