the question that still haunts me: "why did no mother or father ever come forward in almost four decades?"
No parents or relatives living
Foster system
Parents didn't know where to look, still don't know where or how to look. There weren't that many options in 1980.
She left willingly and they have no reason to think she's deceased
They're looking in a different area or the wrong time.
They never heard of this case to know it's her.
They reported her but her report was lost, aged out of the system, or never followed up on
They reported her but got a runaround. Runaways especially weren't taken seriously.
She was wanted for a minor crime and is listed as a fugitive. In most areas LE won't take a missing persons report on someone who's considered a fugitive.
Missing report is there but for whatever reason hasn't been entered into the national system yet.
We have any number of cases where mistakes in the reporting or jurisdictional barriers have caused obvious matches to be overlooked. There was one in Texas where the missing woman was found only a few days later, two towns over, but the connection wasn't made until the year I joined Websleuths. A girl in California wasn't matched because at first they thought her remains were male, and then her missing date was wrong and said she disappeared after the remains were found.
It's possible they really didn't care. There are enough dysfunctional and uncaring families around. But there are a lot of other possibilities too.