Pete, I feel I have to interject here, because you've touched on one of my all-time most despised pet peeves: being accused of something I haven't even done (yet). The pwBPD traits in my life went through a phase of accusing me of futuristic events: You're going to ruin this, you're going to anger me, you're just going to b* anyway so I'm not doing the favor you asked me, etc. It occurred so often that I found myself repeating: I'm not discussing something that hasn't happened. I'm not discussing something that hasn't happened. I'm not discussing something that hasn't happened. (Exit stage left). It's like they assume the worst for every scenario imaginable and enjoy getting riled up over fantasy. You're absolutely right, it's part of the victim narrative that they are creating. There's some delusional thinking too.
It's funny and rather cynicism inducing, how predictable it all is.
One pwBPD (mother) used to accuse me from early childhood onwards of things like putting her in a nursing home, or causing her death - things I self-evidently could not have done. Another (uBPDx) would spiral into a self-pitying lament about how one day I would tell the story of him as just another bad partner - true, but this hadn't happened yet, and only happened as a consequence of his own actions!
Whether they enjoy it in some way - I think in both the above cases there was some relishing of imagined suffering. Whether it's a way to extract certain reactions or feelings from you - pity, guilt, reassurance. It is, in the end, delusional and ridiculous.