Judging by that rather ghastly poem by Kipling, and that equally horrific film Becoming Jane, I suspect Jane Austen as a woman in her forties was seen as someone who'd outlived her time for romance and already missed the boat by the time of her death, whereas Emily Bronte can still be a fantasy of a woman cut off who still had a chance of love and marriage. Sexist and ageist, I know, but I can't help thinking that's why the narrative is framed that way.