Given that they don't (often? ever?) advertise Light No Fire alongside the NMS updates, I'd say that the updates into NMS are large-scale playtests of LNF engine updates, game systems, or both, rather than marketing.
I'm not so sure about that, but otherwise agree with your comment.
I'll gently point back to my hunch that many (most?) of the NMS updates are large-scale tests for things they're thinking about having in LNF. Given that it seems likely that both games are using the same engine, it'd make a lot of sense to use a preexisting playerbase for large-scale, no-cost testing of new changes.