"Older age does not cause Alzheimer’s, but it is the most important known risk factor for the disease. The number of people with Alzheimer’s disease doubles about every 5 years beyond age 65. About one-third of all people age 85 and older may have Alzheimer's disease." (emphasis mine)
Perhaps if we beat cancer and cardiovascular diseases etc and see human lifespans reaching 100+ years old, we'll see close to 67% of people at that age get Alzheimer's.
I don't think one should extrapolate this study on a lab-grown human-like tissue to mammals like rodents in the first place. Extrapolation to humans is even more bizzare.
The article covers this question, they think it is just a factor. A funnel towards Alzheimer's that a lot of people still end up getting to the bottom of.
How do you account for the disparity between the massive infection rate and the relatively low Alzheimer's rate?