One speaker talked about how romances are rooted in women's struggles in a man's world. That's true, but it triggered some questions and thoughts about that and historical romance. I'm going to toss them out and I hope you'll argue, expand, spin off them and have fun.
If romance is all about women's struggle in a man's world, then it seems clear that the struggle is more vivid in historicals, where most women in most times and places had far fewer rights, powers, and opportunities than today.
But then, why is the 19th century more popular than earlier ones, such as medieval, when the situation was more dramatically unequal before the law?
(I always think in that cover it looks as if he's doing a push up off her ribs!)