Use of a narrator

I think it’d be faster to list how many noirs don’t make use of a narrator. I just watched “The Locket”, and that one makes use of three narrators with flashbacks.
Why does it fit the genre?
First, because you can never trust the narrator fully. Are they telling the truth? Watch “Detour” (Edgar G. Ulmer, 1951) and see if you can believe what Al Roberts (Tom Neal) is telling you.
Second, because noir tends to be about fate, and having a flashback is probably the best way to illustrate how unavoidable fate is.