Yes, many things can cause dementia. Repeated traumatic brain injuries can cause dementia.

But the leading form of dementia is Alzheimer's. Somewhere in the order of 40% of us are expected to get Alzheimer's before we die. The list of things that have been demonstrated to cause Alzheimer's is much, much shorter.

For the last 40 years, the leading theory about Alzheimer's is that it is caused by the beta-amyloid plaques that are found in the brain after death. This theory has produced exactly zero treatments that meaningfully affect clinical symptoms, despite many drug trial and literally billions in research per year. Seriously, between various sources, we've spent something like a quarter of what it cost to put man on the Moon. (It is hard to make a precise comparison, because a lot of that funding was private.)

This single study represents more progress on effective treatments of Alzheimer's than all of that work combined. The importance of the result should not be dismissed.