What are you going to do with the diagnosis? Charge them higher insurance? Tell em they’re dumb? Prevent them from driving? Give them a cash handout? Better not to know.
In some cases there are easily treatable factors. For example the patient may have a vitamin deficiency. In this case they could feasibly halt their progression towards dementia by taking an inexpensive pill today. Human factors are always the most difficult in medicine. We expect old people to be slow, instead of seeing senility as a slow progression in the presence of modifiable risk factors.
article links to a study where lifestyle changes have a measurable impact on MCI