I'm ok with stories that don't advance the plot, but those stories have to at least resolve their own plot. Arks of Omen built up to this climax where the antagonist got their super weapon and then...well nothing. It just ends. At least with The Lion's return, if you read his novel that more or less is a complete story. Even though he hasn't done anything in the wider galaxy there is at least a story that has a beginning, middle, and end. By the end the galaxy doesn't need to be rent asunder, billions dead, and some new super power in charge of an entire sector. As long as there is some conclusion to whatever plot they started.
Maybe part of the issue is the way they contextualize these releases. The Tyrannic war, the Pariah Nexus, these aren't really stories per se but settings within the setting. They aren't meant to be a story of themselves but more of describing an ongoing conflict that is meant to be used as set dressing for your games. The problem is when the plot gets too specific, bringing in named characters who have their own agendas. Now you aren't just creating set dressing, but creating character plots that people are rightfully interested in learning about. The scale is too big, but I think GW is afraid that if every story doesn't sound like the next apocalypse no one will be interested.