Why does the grandmother in " A Good Man is Hard to Find" constantly reminisce about the past, and in what way does she recall the past and why?

Like many older people, the Grandmother remembers the past as better than the present. She reminisces about it in part because that is typically what older people do, but also because she has low status in the family. Her low status is indicated by the fact that she sits in the back seat of the car with the children, they are allowed to be rude to her, and when she wants to visit an old plantation, she has to manipulate them into asking to see it before their father, Bailey, will agree to turn off the main highway to look for it. The Grandmother uses the past to critique how her grandchildren behave:

 "In my time," said the grandmother, folding her thin veined fingers, "children were more respectful of their native states and their parents and everything else. People did right then."

In the Grandmother's memory, the past was a more gracious time when people could be trusted and ladies acted like ladies. She still dresses like a lady, complete with swiss dotted dress, lace collar and cuffs and a hat, whereas her daughter-in-law wears the more casual and comfortable styles of the 1950s.

The Misfit, the murderer rumored to be lurking in the area, represents the unstable new times in which a person can't be too careful.  As the Grandmother says to Big Sam, who owns the burger joint where the family stops for lunch, "People are certainly not nice like they used to be."

We may suspect that the old days were not that great,  but we find out for a fact that the present has its horrors.