Selection bias could be the cause. But artificial sweeteners trigger insulin: A) Short term they move sugar into non-brain cells, causing relative brain hypoglycemia. B) Long term they drive insulin resistance, with or without meeting diabetes criteria, but cognitive decline expected.

Like much of human nature, it’s a question of trust - just like when elevators first switched from human operators to automation. People were skeptical, even afraid. Now, no one asks for a lift operator.