I mean so what if she had a bad past and started having sex and doing drugs at 13, right? So what if she cheated on her last BF 5 times and whose dad is dying of kidney failure at 44 because he is a raging alcoholic and whose mother used to have a coke habit.. Maybe she just wasn't into me.
What you're saying is: we can speculate and attribute her not being into the guy for a zillion reasons plus one when we go back into her life history. True.
And the thing about finding a basis in her history that may account for her behavior today, is that, once discovered, it still won't change anything. It's like finding the reason you can't pitch a ball today is because you broke your arm when you were 12. Now that we understand why you can't throw a ball properly, it still doesn't change the fact that you don't throw a ball properly.
Bottom line is that you're not going to be one of the top choices for the softball team, because we see how you pitch. We don't have to know at all why you pitch badly in order to make that decision.
Similarly, we can bottom line a girl's BEHAVIOR and make a decision based on that without knowing at all why she acts that way.
But we're human, and curious, and we like to know and understand the why of things; know what we're dealing with. There's some value in that. And that's why we explore things like outer space and BPD women.
I should add this however: if you know a gal's got a big f@ckup of a past, that's a huge red flag that she's most probably seriously damaged, and/or doesn't make good choices for herself, and doesn't qualify as LTR material. We're taught to think of the past as not relevant to the present or future ("But all that happened BEFORE I met her. It doesn't matter. That's in her past!"), but that's not the case at all. A person IS their past. The best indicator of future behavior is past behavior, because that's ingrained for years and the easiest behavior for them to resort to.