That’s just a technical problem; the raw editor could make it available to the DAM program in various ways (eg embed a decent preview jpeg in the xmp). Currently this does not happen.
Everyone would be better off if the DAM and the raw editor were separate. Darktable devs would not have to maintain something which is essentially orthogonal to the core functionality of DT, while people could pick whatever they prefer from a range of DAM solutions (from “I just put files in directories” to “I maintain an extensive and sophisticated tag cloud collated with geolocation data”).