Argyle, I can't speak about the others, but RM had some issues by 1970. His filming and directing style was pretty well known by then. He was very rough on the acting crew, and especially leading ladies. I know that he tried several times to get Roberta Pedon to work in his films and she refused. That was not the best career move, as fate showed, and I certainly wish she had done so, but his style was pretty dominating.
I think I read something about that from Alaina Capri not long ago, too, which was why she basically only made the two films and disappeared. What a loss for humanity, though, Roberta turning down Meyer....
I was only using Russ as an example though. I mean Armando Bo was making a career out of Isabel Sarli, Ponti to a different degree off of Loren....you would think Arv Miller would have had the sense to find somebody to get Joan Brinkman into films. "The Bare Hunt" (aka "My Gun is Jammed") showed that she had some acting chops, enough so that she didn't come across as stiff and wooden, and apparently she made a few other films along the way, but nothing worthy of her stature.
It wasn't just her body, which was deserving, but man, she had some kind of smouldering, sultry and exotic look to her. When Chloe Vevrier started modeling, I was always struck by how much her facial features reminded me of Joan's.