A hypothesis is an unverified tentative insight into something which could be true. Current research is correlating dementia with a wide variety of areas including even personality typologies which are nothing more than statistical clusters of observations.

What I did when I stated this is looked at a number of observations from current literature and asked a what-if question. People unwilling to ask these questions are blinding themselves to entire areas of possible explanations. My hope when posting this was that people might engage with the idea instead of calling it a guess. Retirement, isolation from pandemic lockdowns, isolation from solitary imprisonment, and isolation from death of a partner are all associated with cognitive decline.

There's enough correlation here that it would be worth researching. That's all I am saying, I am specifically not saying my claim is factual just that it is a possible explanation that if true would explain a lot.