Honestly, I think the answer is in your question, if that makes sense. I also suffer from PTSD, but haven't gone through even a fraction of the things you describe. I too, am open and honest about my struggles. I'm also a small woman, very youthful looking and I suppose, present, even physcially as vulnerable due to my appearance.
These types of men sense it and, in my expereince are after one of a few things. Some are just powerless little fucks when feel inadequate, so they do and say things like the victim shaming guy. he's seeking to build himself up at your expense and thinks you won't say a word back.
Others sense the vulnerability and want to rescue the appareent damsel in distress. "Come to Big Daddy, darlin', he'll make it all better." Of course, there are always creepy strings attached and he couldn't even make himself all better, let's be honest. He's looking to make himself feel better about himself too, and hopefully get a super-greatful roll in the hay at the same time.
We are of a similar vintage (I'll be 51 in July). And after years of avoiding, my PTSD seems to manifest itself more as agression toward these types now. I am no longer polite. Not online and not in person.
I loved your story, and thank you for being open and honest about your experience and trauma.