Diet and Dementia

I am simply a person who has resided in assisted living facility for several years as the result of a stroke that affected my body, but not my brain. I am fortunate to have a grandmother who taught me to cook, a degree in biology and to have spent the past 30+ years reviewing restaurants for a newspaper.
I have observed a number of people who have come to this facility, especially men, and within a year gone from "normal" to a Memory Care facility. There is one thing they have in common: their wife or partner passed away or left and they knew nothing about diet and couldn't cook. Their meals then became pre-prepared food or they ate out.
When they arrived here they totally avoided all salads and vegetables, and limited their diet to familiar things like sandwiches with fries or potato chips. There seemed to be a fear of trying something new or different.
I can put part of the blame on the facility for cofusing them with fancy foreign names for common dishes, but mostly it is their choices that are the problem.
I know this is not a scientific study, but only an observation, however I believe there is something in what I have observed.
I have discussed this with a couple of Senior Centers about a cooking class for people who become single late in life, but....