This idea has been around a long time and I felt it was a good hypotheses almost thirty years ago when I was in grad school and saw the reports of aluminum in neurofibrillary tangles.
So, it was not something ignored, but there never seemed to be enough evidence to attribute the cause to aluminum.
My mother was told in the forties to get rid of her aluminum cookware because of my father’s intestinal problems. She never used anything except stainless steel for cooking after that nor did her daughters. The change did have a large impact on my father’s health.
My great grandmother wouldn’t cook in aluminum. She used plenty for food storage etc but wouldn’t cook in it.