In the end it probably because being making pure narrative battletome doesn’t sell as well and that why GW put everything in one book (rules, narrative, lores, and points) . Is both maximise profit and gives as much value as they can for a physical book.
let face it, majority of early access people when reviewing a book often gives a TLDR of the lore and narrative and spent most of their time deep diving into the rules. And this is because their audience and community are just more interested in that content.