Because here's the thing about Jane Austen. She was a very great genius. She is possibly the greatest genius in the history of English literature, arguably greater than Shakespeare. And her achievement is not that much to do with love, although that was her subject matter. It's to do with technique. Before her there are three strands in English fiction: the somewhat mental, directly-reader-addressing semi-oral romps of Nashe and Sterne and Fielding; the sensationalist Gothic work of Horace Walpole and Ann Radcliffe; and the romances of Eliza Haywood and Fanny Burney.
However great these writers are, none could be read now and considered modern. When Austen gets into her stride, which she does very quickly with Sense and Sensibility, suddenly, you have all the key modern realist devices: ironic narration; controlled point of view; structural unity; transparency of focus; ensemble characterisation; fixed arenas of time and place; and, most importantly, the giving-up of the fantastical in favour of a notion that art should represent life as it is actually lived in all its wonderful ordinariness. She is the first person, as John Updike put it: "to give the mundane its beautiful due", and her work leads to Updike as much as it does to George Eliot.
I have no idea how a mainly home-educated rector's daughter came by all that, but I know that imagining her as a kind of acerbic spinster flattens out this genius. It becomes all about the subject matter and not at all about the huge creative advance her work represents.