With a lot of genetic diseases, lifestyle choices can definitely contribute to how early they’re contracted, or whether they’re contracted.

The reason it wasn’t mentioned is because they weren’t studying the mechanism of impact. The goal here was just showing the link between being vaxxed for other things, and having a lower risk for all forms of dementia; it wasn’t to show why vaccines lower the rates. My guess is lower inflammation rates, since inflammation does a lot to us

Edit: The next comment down (at the time of writing) also shows a link between inflammation/viral infections, and dementia