Back in the late Seventies and early Eighties, romance, outside of category Harlequin romances, was a brand new genre, and the early writers were blasting up the bestseller lists while publishers were scrambling to create their own romance lines. Lots of bad writing was being cranked out because publishers were so desperate for content they'd publish almost anyone. Then a group of bestselling ladies decided that the romance industry and its writers needed a voice, a place to nurture newer writers, and protection against the publishers and the torch-bearing troglodytes with their chant of "women writers and books for women bad." RWA was formed.
RWA chapters appeared all over the US, and they taught new writers craft and the business side of publishing careers. The other major writer organizations didn't have an interest in teaching and nurturing new voices, and the Internet wasn't an option so newer female writers of all genres joined in force and learned how to write vibrant and five-senses prose, fully-defined characters, and a reader experience immersion not found in any other genre.
They took these lessons back to their genres and began to publish. Their immersive writing, in contrast to the just-the-facts prose of mystery and science fiction, drew in omnivorous female readers who buy a fortune in books every month, as well as readers who expected more from prose experience because of other media. Publishers and smart writers paid attention because of improved sales and a reader base that was no longer so narrow, and the narrative in most books in most genres changed.
And that is how romance became the mother of the biggest and most successful genre narrative shift in over a hundred years.